Something I'm missing here:

2 contradicts 3 (DVDs you've burned). Do they work or not?

Which software are using to play, Media Player, WinDVD or something else?

Did you install any new software that caused it to act this way?

Anyway, try the following:

Do a firmware update, get the latest version from here http://www.micheldeboer.nl/firmware/index.html

Install the firmware update and see how it goes.

If it doesn't solve it it's better to get a new one; they're not worth fixing and a new one won't cost that much.

By the way, is your PC a Dell and do you have Roxio or Easy Creator?

Sorry, in PCs there is no easy solution; you have to troubleshoot one step at a time.