Ok, first thing you might want to do is change the program you are decrypting the dvds with. DVDShrink is very much outdated for this purpose and fails on many newer protection schemes. I suggest getting DVDFab HD Decrypter (free), or RipIt4Me which is discontinued, but still effective on the vast majority of disks. AnyDVD is another possibility, though not free. Look for software and links in this thread: http://club.cdfreaks.com/f34/dvd-backups-100-free-software-3-5-easy-steps-239933/
Now for your specific problem. As stated in the chat room, an error log from either Nero or ImgBurn might help us identify what is going on.
Are you having any other problems with the drive? Will it play back commercially made disks with no problems? Or burn cds without issues? Or burn data disks?