Power Supply Woes & An Explosion

Well, let me give the run down. I recently bought a new higher wattage powersupply (450 watt foxconn taken out of a new Chieftech case) and a harddrive. I put them into my computer, reinstalled win2k, drivers, etc. Everything was running fine except that the computer seemed to lock up or randomly shutdown/reboot without warning. After a few power failures my windows install was all messed up, so I reformatted and reinstalled. Again, lock ups / power failure. So, I went out and bought a 330W Antech True PSU, hoping to end those problems (and new IDE cables too).

Here is where it gets interesting. I reformatted/reinstalled again without a glitch. I got everything running beautifully. I powered the computer down, unplugged it, and reconnected the power supply hook ups into a less messy arrangement, plugged the power cord back in and hit the switch. Nothing happened. 3 seconds later BOOM! A giant blue flash and a loup pop from the PSU.

what the hell is happening? I'd didn't bother trying to power it on again, and I hope my components are not too damaged. Any idea what the hell is going on? Here are the specs:

Abit KX7-333 mobo
AMD 1900+ cpu
Leadtek GeForce4 4600 VIVO
SB Live Vaule 5.1
Linksys 10/100 Ethernet Card
Western Digital 80 Gb 8mb cache HD
512 mb Corsiar XMS 2700 memory
Lite On 40x CDRW Drive
Pioneer 16x DVD Drive
330 Watt Antech True PSU (busted!)

The previous PSU was a Foxconn 450 watt froma Chieftech case. Before that (when everything ran fine!) a two year old 300 watt antech PSU.

HELP!