A friend of mine built this for me to game on a few years ago.Specs are as follows:
Motherboard: Gigabyte Technology Co., Ltd., GA-770TA-UD3
BIOS: Award Modular BIOS v6.00PG
Processor: AMD Phenom(tm) II X4 955 Processor (4 CPUS) (quadcore), ~3.2 GHz
Memory: 8 GB RAM

Display Device: ATI Radeon HD 5700 Series
Chip Type: ATI display adapter (0x68BE)
DAC Type: Internal DAC (400 MHz)
Approx. Total Memory: 753 mb

Power is 600 watts, It has 1 CD-RW/DVD drive. , as well as a floppy disk drive. Windows 7 Professional 64-bit

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It has begun rebooting itself at random times, . The way it reboots is that the screen will blink out and the computer will simply reboot. Sometimes a blue error screen comes up, but I don't know what it means. It does not seem to be overheating since the computer is not hot and I can get right back into whatever I was doing and may not have another reboot for a while. It is about two years old.
Any idea whats wrongSounds like the power supply, although a Hardware General Protection Fault can also cause a reboot. I'd say try a different power supply after looking in system logs to see if there are any hardware complaints. Sometimes GPF's leave info in the system events log under manage computer, other times they happen so QUICKLY that the system isnt able to record info about them.Hi Redbird;

You say that sometimes a bluescreen is visible? it is possible that it is not sticking on these SCREENS due to it being set to automatically restart.

Follow this guide http://pcsupport.about.com/od/windows7/ht/automatic-restart-windows-7.htm

And then next time it bluescreens; write down the error CODE you receive.
The code should be near the bottom and look something like this: 0X0000007E (0x00000000, 0x00000000, 0x000000000, 0x00000000) (and a driver name if it is specified, usually a .sys, .dll, .ini file)

As well as the text string at the top, which will be in all capitals and have _ where the spaces should be; eg:
DRIVER_IRQL_NOT_LESS_OR_EQUAL

After getting those details we will be able to provide a more in DEPTH analysis

Kurtis