I have a computer I built over 2 years ago. It's used as an HTPC/Video Surveillance system. I usually leave it running 24/7 except for shutting it down once a week for a few hours to cool off. As time went on I started getting lapse and was leaving it running for much longer than a week (can't remember how long since I wasn't on top of things). Recently, I noticed a burning smell coming from the case. It kinda smelled like electrical components overheating. It was very strong as I smelled it from across the room and it took a while to narrow it down to the case. At that I point I shut it down for the night. When I went to start it the next morning the lights came on and the fans began to turn for a fraction of a second and then stopped. At this point if I press the power button again nothing happens. I have to unplug and replug it in (or turn off and on from the PSU switch in the back) and then if I press the power button in the front again I get the lights and fan for a fraction of a second and dies again.
Before I start pulling stuff out of my case I want to see what you guys think.
CASE ROSEWILL|R604-P SL RT
MB GIGABYTE GA-EP45T-UD3P 775 P45 R
VGA SAPPHIRE 100254L HD4650 1G RTL
TV TUNER HAUPPAUGE|1128 HVR-1800
PSU OCZ|OCZ700SXS 700W RT
CPU INTEL|C2Q Q8400 2.66G 1333 R
2 x MEM 2G|KST KHX13000AD3LL/2G R
(HTPC) Seagate Barracuda LP 2 TB ST32000542AS
(Video Surveillance) Seagate HD 500G|ST SATA2 ST3500320SV
(OS) Seagate HD 160G|ST 7K ST3160813AS
DVD BURN PLEXTOR|PX-806SA 20X
GeoVision GV-1240 8 Camera Card - 240 FPS
SURGESUPPRESSR TRIPPLITE TLP1008TEL
I just had a problem with a system that I just built doing the exact same thing, so I figured it was the powersupply. I ordered a replacement power supply and a power supply tester. What do you know...when I tested the power suply it tested out fine and the system exhibited the same symptoms with the new power supply.
So I started taking parts out of the PC. When I took the wireless card out (it's mini-pci-e) the system would start up just fine. It turned out that the mini-pci-e card was shorting out some pins on the bottom side of the pci-e socket that was causing the problem. So a little electrical tape on the bottom of my mini-pci-e wireless card, and now the system works just fine.
In your case, I'd take out your components one at a time and give them the sniff test, if they smell burned that'd be your problem. Bottom line is, you want to identify which component burned out because it's shorting out your system. If course it could be your power supply.