what brand DVD-ROM is it and have you installed the latest firmware updates for it? It sounds like Window may be schizing -out trying to figure out what's in the player. I had that problem with a Pioneer DVR-A06U burner that a firmware update cured. Then again it could be a defective drive. Is it new?

yepp it really seems to be defective ....
from what you told me ...
the last chance is .... take the drive to a friend ... insert it there and try to read the same DVDs not working for you ... will it work there ?
if not ... RMA ... if yes ... you PC sucks :D

The drive came with a fully built PC, which I then changed over the years

I have installed the Samsung firmware update service, but it doesn't find anything new for the SD-612S.

This might be the DVD (disc) that defactive / incompatible, try other piece of DVD, or different brand.

I don't mean to sound like a smart-ass but have you considered upgrading that DVD-ROM to a DVD burner? Since they are now under the $100.00 price ceiling (I saw a Plextor 708A retail box for $123.00 including shipping this morning online. Not the cheapest but the best for the price by far) I'd get whatever burner looks best for my budget and have a nice new freshly warrantied piece of hardware that WILL play/record on almost anything burnable with the latest firmware update...

Yeah, but I don't have that money and my dad won't give me the funds. I'm only 15 you know :)

*L* looks like ya gotta go mow some lawns or fix one of your local business's hosed systems and get a few bucks little bro., I was pumping gas at your age. Try different media or try re-flashing the firmware upgrade, maybe something got schizo'd out somehow. If it's not right now you've got nothing to lose at this point. Good luck to you...