Don't have your prob (so far). Silly Q I know, have you got the MSI Geforce 128 MB 5900 connected to the psu (via molex)? I only ask because someone I know was having trouble after installing the card, and when I looked she had forgotten to connect to the power (no cards she had installed before needed this). Also, does your psu have enough juice to run everything connected to it?
Hope this is of some help.