System keep on reboots

Press the WinKey + Pause
Click Advanced and under Startup and Recovery select Settings.
Uncheck Automatically restart.
Click on the dropdown arrow under Write debugging information.
Select Small memory dump (64 KB) and the output is %SystemRoot%\Minidump.
Restart the PC normally as this will allow the System to Blue Screen and create the Minidump.

Minidump Files can be found here. C:\WINDOWS\Minidump\Mini122707-02.dmp

How to read the small memory dump files that Windows creates for debugging

http://support.microsoft.com/kb/315263

To download and install the Windows debugging tools, visit the following Microsoft Web site:

http://www.microsoft.com/whdc/devtools/debugging/default.mspx

Instructions on using Windbg.

Open Windbg and select file, Symbol file path and browse to the Symbol folder that you have downloaded and installed Symbols to, select OK.
Close the workpage and save the Workspace information. This should lock in the Symbol path.
Open Windbg and select file and select Open Crash Dump then navigate to the minidump, highlight it and select Open.
There are two ways to use !analyze -v the easiest is to click on !analyze -v under Bugcheck Analysis.
When you have ran the initial dump if you look to the bottom of the screen you will see kd> to the right of that type in !analyze -v and press the Enter key.
Ctrl + a will let you copy the information and paste it into notepad.

Look to the bottom of the page for information like this. This was fixed by updating the Graphics Drivers.
FAULTING_THREAD: 864f6a98

DEFAULT_BUCKET_ID: GRAPHICS_DRIVER_FAULT

CUSTOMER_CRASH_COUNT: 1

BUGCHECK_STR: 0xEA

PROCESS_NAME: logon.scr

LAST_CONTROL_TRANSFER: from 00000000 to bfef0fea

STACK_TEXT:
f6434e6c 00000000 00000000 00000000 00000000 sgiul50!DrvBitBlt+0x585

STACK_COMMAND: .thread 0xffffffff864f6a98 ; kb

FOLLOWUP_IP:
sgiul50!DrvBitBlt+585
bfef0fea 75f9 jne sgiul50!DrvBitBlt+0x580 (bfef0fe5)

SYMBOL_STACK_INDEX: 0

SYMBOL_NAME: sgiul50!DrvBitBlt+585

FOLLOWUP_NAME: MachineOwner

MODULE_NAME: sgiul50

IMAGE_NAME: sgiul50.dll

DEBUG_FLR_IMAGE_TIMESTAMP: 3b7dfec7

FAILURE_BUCKET_ID: 0xEA_IMAGE_sgiul50.dll_DATE_2001_08_18

BUCKET_ID: 0xEA_IMAGE_sgiul50.dll_DATE_2001_08_18

There may be a clue in there as to what is causing the restart.
You should also (perhaps only temporarily) turn off automatic reboot on error. This can be found through System Properties, Advanced Tab, Startup and Recovery, middle section System Failure - Uncheck Automatically restart.

If there are no events and no Blue Screens, then heat may be the issue (although normally that would be a hard shut down).

can cause a pc to reboot like u described

the main causes in my experience are in this order.

overheating, cpu heatsink is covered in dust bunnies or fan has failed

failing main board, swollen capacitors around the cpu.. capacitors should be perfectly flat on the ends where the k or + mark is and not have anything leaking out of them

failing or not properly connected RAM
if u wiggle the RAM a bit, NOT to much, and the computer reboots, it's probably not connected properly or failing, it can be removed and the gold contacts cleaned with a pencil eraser, then wipe any remains of the eraser off with a soft cotton cloth,
re-install and re-test
run a check on the ram...
http://oca.microsoft.com/en/windiag.asp

other addin cards not properly connected or failing, wiggle test again, if it reboots try
cleaning as described above

poorly connected cables or an open in a cable
again the the wiggle test on all cables can often reveal the problem child

malware

I use and old Beaver Paint Sprayer. With the paint can disconnected and one of the fittings to reduce and direct the air flow it is a little beauty. Being airless there is no moisture involved whatsoever.

You can guide the air and use the paint brush on the USB ports etc.., also use the brush handle to stop fans from spinning as the air is directed around them.

I bought this unit in 1992 and over 3 years painted my house with it. I have had to replace the hose but I ended up with a longer one anyway that saves having to move the unit so often as you move from PC to PC. The paint can is not used anymore as the seal is gone. I replaced this unit with a 2 1/2 HP compressor for painting these days so it is perfect for cleaning PC's.