Hello welcome to GeeksToGo,
Hope fully I can be of some help to you.
I'm going to need more info about your computer
The MOBO model number
Ram speed and capacity
HDD capacity and type Sata/ide
CD\dvd rom type sata \ide
and the power supply wattage
I'm not sure about your problem, How long has it been unstable? Had it been showing signs before this.
Did you install any new hardware or software?
Have you Overclocked your system?
Do a check of all connections:
Power both ends
20+4 power connector on the mobo
4-8 pin 12v tail on the mobo
all ide and sata interfaces both ends
power to all hdd and Cd\dvd roms
check to make sure all fans are spinning up to speed if not fix them
if any problems can't be corrected don't continue till resolved please.
For the sake of trouble shooting if you have more than 1 HDD remove the secondary slave, (the one with out the Operating system)and 1 cd\dvd rom disconnect the second one. if you have any video cards remove them unless your Mobo doesn't have onboard video, just make sure to enable onboard video before you remove your Video card I would say for right now, remove all but 1 RAM module, The one next to the CPU is the one that should be occupied.
Try to reboot if it still screws up, change the Ram modules around and try again.
if that still doesn't work
Then run Memtest 86
follow the directions on the link to create a boot CD or floppy. Run the test for at least 5 passes on 1 Ram module, if you come up with no errors, then switch the ram modules and repeat the test. After both test are complete, Place the other Ram module in the second slot and run the test again with the same specs. If that test comes up negative then the problem doesn't lie with your ram.
Post your results in your next reply, +\- errors what works and what doesn't
Edited by cbarnard, 27 March 2009 - 02:36 AM.