PC restarts

As soon as i press the on button on my pc, the white whiting comes up with black background (dont know proper name) then after that it goes to a black screen for about a minute, then pc randomly restarts, it dones this maybe twice, sumtimes 3 times untill it finallg goes theough to welcome screen then desktop, ne ideas wot it could be?

Cheers

It could also be a small crack in a solder joint (I would suspect the PSU). As the equipment heats up the crack closes and the fault ceases to have any effect.

You should check all the connections first though, if they aren't completely tight the same thing could happen.