Not sure it's the motherboard, but it shuts itself down. Bios reports that the CHS fan is not running. Don't know which one that is? Have cleaned the pc out good and reseated the processor with fresh thermal grease. Temp starts out @ 20 degrees C and rises fast within a few minutes of running time. Afraid to leave it on too long at a time if it is a heat issue. Can you help me? Today it told me that the temp was lower than normal but it was up to 27 degrees C at the time...???

make sure that you have the right heatsink fan on the cpu

sure it does all PCs do that, full of lint, all do.
we clean it.
it has fan and vents
all fans all vents and heatsinks must breath or it overheats.
all do that not cleaned, drive your car around with the radiator blocked, boom.
all PCs run slow overheated, by DESIGN.
this slow down , reduces heat, and saves CPU/GPU burn up.
just like my chevy, truck, it cuts cylinders to save the engine.
same deal both.

same deal; same reasons.

http://www.pcdied.com/overheated.html

it sounds like your motherboard is shutting itself off to protect itself from overheating or some other system failure. you should verify all your fans are running at the correct speed. if it seems like everything is running fine, you can probably turn that off in bios. obviously if there is something wrong with the fans, then you need to replace them. Another options is maybe the processor is getting too hot which is why it's shutting down. open the case and remove the heat sync from the board so you can see the processor. clean the thermal paste off the processor and apply a new generous layer. put the heat sync back on and then try and restart. make sure before you do ANY of this you unplug the computer! good luck and let me know if it works!

If you need further help, reach me via phone at https://www.6ya.com/expert/joel_63c670a84e9f6a97

avoid geeks, try real shops , they are NOT.
it is overheating
and all PCs every made do that, if not serviced
ever heard of service? like a car, like oil filters and air cleaner.
same here but no filters
we clean the vents, and all air paths clean.
never use it on a a blanket blocking vents the go to geeks and it works. ok.

load program that reports, CPU/GPU heat.
see it overheat sure, over 50c is too hot.
and needs service or off that blanket.
i cant watch you use your LT, so.... only you know what you do.
use a desk, or better buy a bottom plate with fans added.
I have a fan plate platform that i use on my hotter running I7 LT's

if the CPU overheats the CPU will shut itself down , by its self
Intel or AMD magic, does that.
the BIOS will see it overheat and crank up fan speeds.
if the venting system is blocked, there is no HOPE NOW.

all PCs must breath, or they overheat, all do.

It could be overheating. After it shuts down, restart it, and enter BIOS SETUP, and look for a "PC Health" or "Status" entry on the menu. If you're lucky, it will report the current CPU temperature, and the speed of the fans, and the settable temperature at which it will shut itself down.

Check the capacitors on the motherboard -- any capacitor with a "dome" on top, instead of perfectly-flat, is a leaking capacitor that is intermittently failing.

sounds like either the fan on the cpu is giving trouble or the power supply itself. remove the cover and observe the fan to see if it is working properly also check the fan in the power supply. replace as necassary

sounds like you may have installed the wrong bios. Did you keep a backup copy of the old 1. You should have been prompted to save a copy.
Second thing is to report exactly what was said in an error message..."something/something" really does not cut it.
Lastly it maybe that your mobo just fried itself.One should not just go to doing a bios flash unless absolutely neccesary.
You might try to restart and enter the bios again and click on the install default tab and see if it will restore the default settings. You may have to reset the date/time settings. then save and exit. If the cpu fan does not remain running shut down immediately and try placing a house fan to blowing directly into the pc and try to reboot again. If the cpu fan shuts down again then you probably blew the mobo

If the fan isn't running, the computer probably shut itself down because it overheated. Check to make sure the cable going from the fan to the motherboard is securely plugged in. If it is and the fan still doesn't run, you have a faulty fan and need to replace it before you start up your computer again. It's not good to run a computer that hot.
Please rate, thanks!

Please Check CPU making any noise or not.

remove the CPU side door and check Fan is rotating on Processor if not it may not rotate due to heavy dust inside. ( clean it and refix it)

Check SMPS Fan is rotating or not..

If fans or not rotating Heat Builds up then computer shuts down itself.

If both fans are working...Just Open BIOS window by press DEL button continuosly while startup and wait for 2 to 3 minutes If the computer shuts down Itself in BIOS Window also then we can confirm issue with Hardware.

If Computer not shutting down in BIOS Window then issue with Operating System Boot files corrupted.

While Turn ON the system press F8 to enter in Safe Mode.

Open command prompt by clicking on

Start >. RUN >> type cmd >> then press enter.

now type chkdsk /f

now press Y

then reboot PC it fixes the Boot files error then your PC works perfectly.

If you still exp same issue let meknow..

Random rebooting, without know the history of your PC all I can do is give you a list of things to try and look for. The first thing I would do is check the basics, if that turns up nothing then the only option left is to removing variables one at a time. Obvious things to look for: - Physically remove and clean the processor heat sink. Make sure the area directly underneath the CPU fan is clean of dust; you have to remove it usually to make sure. When you reattach the heatsink take the opportunity to clean off the old and reapply new thermal grease. Use sparingly to ensure excess material doesn?t get on the CPU pins or the motherboard. - If you have a video card with its own heatsink and/or fan make sure it is free of dust. Make sure the fan runs freely and forcefully. It usually takes a can of compressed air to clean the dust underneath the fan, in some cases it requires disassembly. - Make sure all connectors are snugly plugged into their sockets. - Make sure all cooling fans, especially the power supply are running smoothly and forcefully. - Vacuum out case air vents and blow out dust from all secondary heatsinks and around the memory modules. - If your computer is plugged into a power strip or UPS try plugging it directly into a tested wall socket. - With the computer running try wiggling where the power cord plugs into the PC and the wall socket. If nothing turns up the next step is to make this computer as basic as possible. Disconnect any secondary drives, all USB devices, hubs, ports, printers anything you can remove and still have the PC boot. Don?t assume something couldn?t possibly cause this, making assumptions works against you. Run the machine in the basic mode and see if the problem persists. If it doesn?t don?t assume its one of the things you removed, replace the items one by one remembering it could be a power problem that only manifests itself when lots of stuff is plugged in. If the problem persists try these one at a time: - Typically your system BIOS will have a safe or factory reset mode, set it to that making note of the setting you had originally. - Try removing the hard drive and boot via a CD (Windows install or a diagnostic disk will do). - If you have a plug in video card try using the motherboards built-in video or another know good video card. - Test or preferably replace your power supply with a known good supply. - Try new memory. - At this point we?re probably left with just the processor and motherboard which means unless you have spares around you?ll need to start considering if its time to upgrade to a new motherboard and/or processor. Also if you haven?t done so already you should immediately backup (and test) your important files stored on your computer. The random shut downs are dramatically increasing the chance your hard drive will suffer damage or data corruption. I hope this helps but let us know if you have any other questions and please don?t forget to rate this post.