Power Supply Meltdown

Hello all,

I had a serious problem the other day with my power supply. I had just finished building my PC (this being my second ever built so I'm far from an expert) and after turning it on restarting once and entering the BIOS the power supply abruptly blew up. Everything seemed to be working up until this point. The computer had ran for about 2 minutes before this happened. Loud crackles and blue sparks shot through it for around 3 seconds or so and then the power went completely off. I'm baffled at what I could have done wrong since I followed the directions perfectly as far as I can tell. Has anyone heard of this happening and if you could please give me some suggestions on what to do next I'd appreciate it greatly.

Thank you!

System Info:
300Watt Power supply (probably a cheap one at that)
xp2000+
Geforce4 ti4200
40x MSI cdrw
40gig Hd
Corsair 256 mbXMS ddr333ram
3 case fans
Gigabyte GA-7VRXP