by DVD Player do you mean DVD Rom/R/RW drive ? or DVD playback software ?
If it's the drive I'd try pulling out the data cable (either IDE or SATA) and replugging it back in, could be that it's come loose. You could also try 'reseating' the power lead.
If it's the playback software I'd try uninstalling and reinstalling it. If that doesn't work try a free player like VLC or Media Player Classic.
If none of that works then you might want to think about formatting your HDD but seriously I think that's overkill for this problem. Course it's less expensive than buying a new DVD drive or new connection cables but it's a LOT more hassle.
It also could mean your dvd drive went bad. if it plays dvd but does not burn dvd or cd. guessing you are using windows. if you are you can try CDburnerXP. this is my number one windows burner. Think formatting your HDD drive is not needed. if you move you system a lot cable tend to come loose check those.but I think your drive has partly died. Plus you do not format CD-R OR DVD-R.