hp 5300 1 g ddr2 - Think you got the deal from slick. Impossible price.
bfg pcexpress 128 mb vid card - What's it exactly? Look at the package.
Does your ower supply have a 24-pin mobo power cable? Plugged in everything from 24-pin mobo, 8-pin cpu, any 6-pin video, etc.? Is everything totally inserted? RAM, video, other pci cards.
In the mobo manual, what minimum psu wattage does it recommend? It should be in the 24-pin mobo power connector section or before that.