while burning cd-rs the system works fine ,but burning dvds I get power calibrtion error help:Z:Z
Power calibration error. That's one of the first signs of a dying burner. You can get a few more burns out of it by reducing your burn speed, but I'd start looking at Newegg for a replacement.
Please post an error log, and make sure you are using Nero 22.214.171.124:
A firmware update to your burner, or an update to Nero, may solve the problem.