Testing the PSU is a bit out my expertise, but basically getting a meter and checking the voltages. If you bought the PC as a unit (as opposed to building it), may be worth taking a look at the PSU inside. Quite often box shifters put in a cheap PSU as good units are expensive. At the end of the day its the most important part of your PC, if that fails or goes pop then it can take everything else out with it.
Can you test your dodgy drive in another PC? If not at home, then maybe a friend or at work?
As for a replacement, I bought one of these
Laptop USB Blue-Ray Disc Burner Writer player Drive BD on eBay (end time 19-Mar-10 16:50:27 GMT) from this seller. I am replacing all my rigs with Acer Revo's at the moment so wanted an external drive I could move between PC's. Have to say its a lovely bit of kit, maybe not what you are looking for though.