I cannot burn DVD's

Have you tried the usual..

Mac OS X: Starting up in Safe Mode

http://support.apple.com/kb/HT1455

Resetting your Mac's PRAM and NVRAM

http://support.apple.com/kb/HT1379

Resetting the System Management Controller (SMC)

http://support.apple.com/kb/HT3964

Just to make sure that your Superdrive is not the problem, download the BURN software and burn a test VIDEO DVD...

http://burn-osx.sourceforge.net/Pages/English/home.html <<< click here

i think it should be either dvd super drive having problem or software problem try to use toast titanium or other burning software which is compitable with mac os and can you check if the sper drive dvd is reading other cd or not