Possibly power supply problem I would say. Could be failing, or premature power_good signal being sent.
If you have a spare PSU try that instead. If you have a voltmeter you could check the PSU. If you hare spare cables you could try swap some (especially the mobo pwoer 20+4) If you have neither, then it's a bit hard to diagnose. Check to make sure the PSU cables are properly plugged in at both ends.
Could also be a problem with the outlet, try plugging it in to a different power outlet.
Do you hear the HDD spin up? Did the problem start after you reseated/pasted CPU?
May as well check your ram is properly plugged in (you have to push pretty hard until the plastic clips flip in to place).
Maybe check BIOS settings to make sure everything is as expected.
Does the problem exist when resuming from standby, hibernate, cold boot, or some combination? About how many tries is numerous?
Sounds like an annoying problem...