When I start the PC, it shuts down just after the fans and things start, so after 1 second.
Strange enough, it will boot normally, when I take out the main power plug for a few minutes(most of the times, but not always)
Rebooting from windows 98 or rebooting with the power-button will shut it down again after a second (so I have to take out the power plug again).
I don't remember what, but while trying to solve this, I changed something in the BIOS and it resulted in the PC (when booting)continuously starting - shutting down - starting again, shutting down and so on.
Removing the BIOS battery for a while resulted in the first state: shutting down after one second.
This made me think it could be a BIOS problem. Any help would be much appreciated.