Start by making sure everything is seated properly inside the case, and vacuum/blow out all of the dust that you can see.
You can try to see if the board will POST with a minimum configuration (board, PS, CPU, RAM, video source) to see if an add-in card/device has mal-functioned.
If the power supply was excessively clogged with dust, it has most likely failed. Note that the board will not power up if it does not get a "power good" signal back from the motherboard, so make sure that the PS-to-motherboard connector(s) are properly seated.
Moderator - Wim's BIOS
- DFI 586IPVG, K6-2/+ 450 (Cyrix MII 433), 128MB EDO
. BIOS patched by Jan Steunebrink
- Amptron PM-7900 (M520), i200 non-MMX, 128MB EDO
- HP8766C, PIII-667, 768MB SDRAM
- ASUS P3V4X, PIII-733, 256MB SDRAM
- ??? ;)