Nero encoding problem



when using make your own dvd the encoding menu and streams bit starts fine at a good rate of nots but after about a minute starts to crawl and time to complete goes up hours
ive been doing my film files like this for months no probs takes about an hour and a half but now so slow done all the usual things defrag, more space etc etc but im at a loss now can u help me.

p.s. i changed nothing