You're all wrong .
Your PSU (power supply) probably doesn't have enough juice...
I'm probably a dumbass...well I know I am, but I'd try changing it out if you have a spare lyin' around that happens to have more power.
I had this problem with a Win95 computer...an old Packard Bell 120mhz p1 with 32mb of ram.
For some reason whenever I would pop in a nic, it wouldn't boot.
I didn't have any old AT PSU's lying around so I just reformatted the entire thing, pulled out all the hardware, put back only the stuff that I needed, and it somehow worked...
It was an old family computer that I had accumulated and I was trying to pop a nic into it to network it....for some...odd...reason...because it was slow as hell.
Anyway, try that...I'll stfu now.