My computer keeps shutting down irreglarly - Apple MacBook Pro Laptop Computer with Intel Duo Core 15.4 Inch PC Notebook

Have you tried restarting your iMac? If that doesn't solve your problem look at my answer to this question. My computer keeps shutting down irreglarly

Your computer is overheating, it is shutting itself down to prevent damage to the internal components.

Your computer should be serviced by a computer technician. He/she will clean the components and chassis of dust. This will increase airflow over the components, meaning your system will be stable and will not shut down unexpectedly.

Take care!
damnor01

Shuts down when? Right after you boot it up? Or does it run a while then shut down?
If it shuts down after it has run for a while then the computer is probably running hot. Either the CPU Fan is not working or the Thermal Paste has dried up or is too thin to keep the CPU Cool. To prove it is running hot, let the computer sit for a while then boot it up. Once it boots up use it until it shuts down and immediately try to boot it up. If it does not boot up that means it's running hot. But if you let it cool off then try booting up you will be successful.

Computer may be shutting od due to following reasons:

Computer Virus
There are higher chances of a computer shutting down due to the interference of a computer virus. The virus gets into the computer and fiddles with crucial sections of the operating system, which may cause the system to shut down automatically. You need to install a good antivirus software and get the computer scanned thoroughly for any malware and viruses. Also see to it that the operating system and all hardware drivers are updated.

Power Supply
The computer power supply unit is an equipment that is installed in the cabinet to provide power to the system for operation. Your computer can shut down, if there is not enough power supplied to it for handling the programs running. If you are using the computer for running intensive software such as PC games, the system would require more power than what is actually available. Another reason can be overheating of the power supply. After the power supply is used for a substantial period of time, there is a possibility of dust getting collected inside it. And this may cause it to overheat, resulting in the shutdown of the desktop computer. If the power supply is at fault, you may need to get a new one installed.

Overheating of the Motherboard and the Processor
As with the case of dust getting collected in the power supply, the computer motherboard and the processor can also collect dust, which may be the reason for their overheating. This may also be one of the reasons why your computer keeps shutting down and restarting. You need to open the computer cabinet and clean the dust off the computer parts. The CPU board and the processor can also overheat because of many applications running. If this is the case, then it is suggested to keep the running of applications as less as possible or increase the size of Random Access Memory (RAM). Bad capacitors on the motherboard is also one of the reasons, why your computer keeps shutting down very often.

The 'Automatically Restart' Setting
If you are using Windows XP operating system, there is a setting that indicates the computer to reboot if it detects an error in the system's operation. In order to check if this is the problem, click on 'Start' and 'Control Panel', then select 'Performance and Maintenance'. Click on 'System', then the 'Advanced' option, and select 'Settings' from the 'Startup and Recovery' section. You will find an 'Automatically restart' option, which you need to uncheck for preventing the system from rebooting. Read more on computer keeps restarting on its own.

These were the possible reasons, why your computer keeps shutting down and rebooting. You also need to check if the power cables are properly connected to the cabinet and to the UPS, as loose connections can also be a reason for system shutdown. The most common cause of the computer getting shut down or restarted is due to overheating of the power supply and other internal computer parts.

Did u put the FAN to the right CPU FAN board connection? or Align ur heatsink to the processor, procie might have been overheating 'cause the heat sink didn't touch the procie!

replace all leads including IDE and SATA and electrical before replacing a new PSU

keeping it updated dont mean you dont have one when your computer dont shut down there is a parasite program keeping it on you need to check it, anti virus protection only protects against known viruses not one that has not been detected yet, once one is found then a program is made to fight and delete it, not before

thermal shutdown.... it's overheating and you need to make sure the fan is working and clean out the dust and dirt

Robert

At least it doesn't Atomically shut down. that's a bigger problem.


but seriously give us a clue. no computer actually shuts down automatically, you have to push something or set it up to shut down on a timer or something. you've given us nothing to work from.

some ideas: remove the virus, remove torrent programs that might be keeping the computer running all the time, reinstall the OS.

Scan for Malaware and/or Virus.