1) first check for virus 2) if there is no virus then it is overheating.it can be possible that fan is not working properly. 3) it may be caused by the problem of hardware in which a software is corrupted. 4)it may be problem of power .either with your main power line may have loose connection.
First, you've written something but not the conclusion of Restarting Issue! # Your computer might has been injected by a virus! * You can clean it up at safe mode with a Anti-Virus or an Anti-Spy soft. # Your computer's Fans aren't working! * You can look at cables if they are connected correctly and look if fans start working. If doesn't work might your PSU is very less. # Your computers hardware temperature is high (hot). * Correct way to look the temperature of your hardware is entering at BIOS or using programs like CPU-Z, Everest Home Edition. These will detect your computer's hardware temperature and you will be able to know where is the problem! Fixing the problem could be buying more fans, using a liquid cooling system, if you're overclocking you should disable overclock and others staff. # You have a hardware problem! * You can have hardware problems, they cause your computer to do not work. Any simple example is that you've put a video card that require AGP 8x and your motherboard handles latest AGP 4x, this will cause restarts and other issues too. Another example is putting DDR and DDR2 together in a motherboard, this will cause your computer to cannot read both of them because many of motherboards support only one pair of your RAM types. There were many issues like this, esspecially when processors cooler not working it will do high temperature that will cause restarts, or putting wrong hardwares what will cause high voltage what will damage your computer. # Your Windows Files could be corrupted! * You can take a repair with your OS's CD. Like Windows XP's CD just boot-up and start repairing. These are some of reasons what there could be many of them!
