Okay if you have tried re-seating the memory, that's good (suggested by Grimley)
Here is a list of things I made when my PC needed some TLC, I am a rookie by the way.
A quick look also found this and I am reading it now
http://forums.overclockers.co.uk/showthread.php?t=18281472
Re-seating the other items can help, check your internal power cables, graphics card, hard discs, optical drives – unplug them – plug them back in. Check your monitor cable!
Clear CMOS has been suggested by Stulid already.
To clear the CMOS:
Unplug the power socket. The vast majority of newer computers are ATX, meaning that even when the PC is off, if the PC is plugged in it still has power flowing through it.
Press the power switch to dissipate any residual power in the computer.
Either remove the CMOS battery (small round silver battery) for a few minutes, or use the board’s CMOS clearing jumpers. This is simply a wee plastic tab that bridges a connection. Usually there are three pins – when the jumper is over two of them then the CMOS isnt touched. Switching the jumper over for a few seconds clears the CMOS. Set the jumper back, plug in the power and try to get the PC to boot again.
See the manual for your motherboard for instructions on which jumper to move, and to what position.
Often forgotten about:
Do you have a speaker? Plugged into the motherboard - motherboards and BIOS boot codes – check your manual, some mother boards have diagnostic LEDs on them and the beeps are codes!
Still not working?
Run only the bare minimum. Remove all non essential devices etc. All you really need is:
Motherboard
CPU & CPU cooler
RAM – one stick
Video card (unless you have an onboard mothercard)
Power Supply
You do not need:
Optical drives, such as CDROM/RW/DVD/etc
Floppy drives
Any cards, except video card.
You don't need sound cards etc
Hard disks
More than one stick of RAM
A case, although it may be easiest to leave it in the case, sometimes running the barebones on a bench can eliminate problems such as grounding problems etc.
Make sure everything is at stock speeds and voltages.
If the above works, add devices one at a time until it doesn’t boot. Then you have found your problem.
If it STILL doesn’t boot….
Can you test the PSU or do you have a spare?
Try replacing components, I guess memory and motherboard then CPU!
Common Problems
RAM, AGP, not properly seated, gold contacts are dirty.
Bent CPU pin
Smeared electrically conductive thermal compound on a component
PSU switch is off!
Left CMOS jumper in the clear mode
Many boards will not boot if a fan is not attached to the first fan header, as a safety measure.
Screws/pieces of metal can go astray and cause short circuits.
Weak or faulty PSUs can often cause things like random reboots and shutdowns, or can be at fault when the PC will not start. If you get these sort of problems, check your voltage rails using a program like Motherboard Monitor or Speedfan.
Bad RAM can also cause many weird problems, such as random crashes, reboots or spontaneous and random errors. In the event of such areas, try a different stick of RAM to see if the errors go away.
Fingers crossed a system check gets it up and running
pod
