Hi Kanzi,
I suggest to try the following
1) unplug everything from the mobo and leave only the CPU and RAM (unplug any PCI card, PCI-X card, SATA cables, Floppy cable, IDE cable, make sure no USB device is plugged)
2) Turn on the PC.
If there is POST, RESET the PC a couple of (use the RESET button, do not turn it OFF and ON), if continue posting, try to turn it off and after 2 minutes on again. This is to make sure is not PSU related.
If there is NO POST, make sure the PSU is firmly connected. Still no POST, change the PSU, still no luck, swap the RAM and lastly the CPU. Still no POST? You have a dead MoBo.
Remember, turning on the PC and seeing the fans work, doen's mean the PSU is OK.