I had a problem with my Dell vostro 400 desktop machine, in that my frame rate was way down when in gaming, & also a strange occurence at start-up.
I would switch on, the blue light appeared, the fan came on at full speed as normal, but as the fan slowed down the light went out & the computer was dead, then it immediately started up again, then died down, & on the 3rd time the bios bleeped & it stayed on. This was driving me mad, i trawled everywhere on the net & all seemed to point to faulty power supply, others said faulty motherboard, but i wasn't fussed on installing new power supply as it was about £80 for this model. Incidentally the graphics card was a nvidia geforce 8600gts.
I finally took up a friends suggestion of a gainwood 9500gt 1gb DDR2 graphics card which only cost around £50, & it is absolutely brilliant. My fps went way up & the machine starts first time.
On the start-up issue, this new card takes power only from the pci express slot, not from a flying lead, so whether that was part of the problem, i don't know. The card has no fan so i thought it may get hot as on the vostro midi tower it is upside down, & also takes up 2 slots, but it has been fine.
So if anyone has had similar problems as i had, i hope this has helped.