i think i just found my problem.
When i plug in the power cord in to one of those mini-tower, the fan in the psu starts up full blast for about one second. Its like a car doing a rev, always tought it sounded kinda cool .
I just notices it dosent do it anymore when i plug it in, so im gesing its the psu .
Problem is ,since its a mini-tower, the psu is a custom shape, ikinda like this:
http://cgi.ebay.com/BRDNEW-DELL-DIME...QQcmdZViewItem

To bad, cause i happen to have two standard psu.

oh well