The PSU fan does not run, computer shutsdown.

that is a very old mobo, emachines is owned by acer.com now.
forget booting that last and means to an OS, like XP?
this PC is 14 years old. now and the coin cell battery is dead,located just below x16 PCI-e slot. flatsocket
first is that and next is get you monitor working with BIOS pages DEL key is the hot key to BIOS.
booting is last,(the OS boots last)

power is first and all fans working
PSU 24pin and that 4 pin power jack to CPU jack must be both connected.
the jumper (many) on the mobo must be set correctly the manual is found googled.

Use the VGA port on the MOBO rear.
the PC power lamp must glow turned on at power switch.
the fans must blow. all . must.

then the BIOS flash screen shows next and then POST error, if any
and list BIOS boot order set to HDD0 first. top of list , if the HDD is good it boots 14 year old OS, that is fully infected as all are XP.
got DDr2 RAM?

the goal is get bios working first and no coin cell lasted 14 years not one, sorry, 7 is spec max
1/2 that parked in a box the attic,


In BIOS new coin set time and date, and boot order. if it will not boot.

There are two types of PSU (silent an ordinary) so original PSU is silent.

"i can find my dmm?" did you mean CAN'T?
"its clearly off", what is off?
the fans are 3 pins,2 are power, one is RPM tachometer.
"it all works fine", so you can boot and run any OS, ?

"the voltage reads +12vdc", where, at fan or PSU?
the fans run off 12vdc, they are DC motors (from outside fan)
if the fan runs slow at 12vdc the the fan is bad or is a low RPM
fan, as some are, bigger fans run slow, for less noise.!

first is the CPU fan it must run full speed, if not the CPU will overheat in seconds and ALL CPU shut them selves (by there selves) this way. so CPU fan is first. what does it do... there....?

then BIOS screens. GOT BIOS UP? and running? with, ESC key pressed>.
let me guess your symptoms
1: PC dead. will not boot.
2: BIOS dead.
3: all fans DEAD,.
4: power switch works and all PSU voltages read right, (seems not)/?
5: if the PSU power wire reads right(DMM), matching the side sticker voltages, and the CPU is dead, the MOBO is dead, or CPU is toasted.


here is a modern PSU, sticker.
see 5 to 10 power lines, see them. all must read correctly
if a fan is dead, then its dead if 12vdc is present on the fan power pins.

Hi.

If there is no sign of life, then it is usually a power supply problem. Check PSU connector. If PSU fan does not turn on check the power cable. If power cable is good, test power from PSU using a multimeter and eventually replace PSU.

Yes. Got RAM? The heatsink fan? How about a video card, and all the 12V (4 to 6 pin) connectors? All plugged in suitably?

hi! if your pc is still powering then theres no problem with the PSU, if your pc boot and have a display on your monitor then theres no problem with your VGA card and RAM but if your PC don't have display then you must check your VGA and RAM it maybe a faulty hardware. and next thing you do is check if your HDD is stillworking and make sure you have a bootale CD with you..good luck

If you don't hear anything on bootup then it is most likely the power supply and you can purchase one from your local Best Buy Comp USA type store. It is very easy to replace if you have repair/troubleshooting skills. I can elaborate if you want to give it a try but it sounds like the power supply that is bad.

Hope this helps,
TankMurdock

I agree with ****. You have to replace new PSU .

Remove and reinstall memory.

how many video cards do you have installed?