PSU's keep shorting out!!!

Here's the situatin:
I had a 400 W PSU, everything was fine, I got a DVD burner and burned a couple things, then one day I was burning a DVD, I left the room, came back a few minutes later to check on the progress and the computer was off. The PSU went bad in the middle of the process. Luckily I had an extra 400W on hand so I put it in and everything was peachy again. Two days ago I was playing HL-2 and the computer just shut off while I was playing it. I went out and got a 500W because it was on sale and it works, but I didn't hook up the DVD burner yet, I am waiting for some feedback as to what the source of the sudden shortages could be.

160 gb HDD
40 gb HDD
CD burner
p4 2.8 gHz, 800 FSB w/HT
floppy drive
radeon 9800 pro built by ATI
512 mb pc3200

I did the PSU calculator at a couple websites and the most I got was 333W minimum, and I know that 400W should be more than enough, so I am kind of looking suspiciously at the DVD burner because everything was fine until a few days after I got/installed it. It's a 'micro-advantage' 16x max +/-R/RW. Please help! I don't want to keep flying through PSU's!

 

What brand PSU's were they, Generic?

 

Yes, they were both generic. The new one that I got is a Mad Dog though. Are you thinking that is the problem? The old ones only had one fan each, but my new one has 3...

 

3 Fans? You might need to tie your PC down so it doesn't take off!
Anyhow, even though I'd never recommend using the generic PSU that comes with no-brand PC cases they should still not be shorting out on you (and twice?) given the fact that the PSU was sufficient enough. Make sure you are using a solid surge protector (preferably one with 1800+ Joules protection) or a 325V+ UPS unit. Make sure your mobo is properly grounded and the connections from all the devices to the mobo, including the case LED/switch cables are properly connected. Make sure you dont have any loose naked wires or screws in the case, etc...

 

Alright, thanks! I know there aren't any screws in the case, but I'll look into surge protection etc. and make sure my gear is grounded.

Thanks again