Nero Hard Drive Speed Problem

I have a 60 GB 7200Rpm WD hard drive and a 48X Lite-On cd burner, and when i first hooked it all up and did a speed test in nero, it used to read in the hundreds (140X…etc…) , which made 48 burning quite easy, but now whenever i do a speed test in nero it stays at about 36X, which is only usefull for burning cds at 32X and under. I would understand 36X if it was an audio cd, but im trying to burn cd images and data files. Can anone tell my why my hard drive isnt reading as fast as it used to??..Programs like Sandra and other benchmarking programs shows my drive reading at about 30MB a second, so i dont know what the problem with nero is. Also i have about 20 gigs free, so its not like it has no space.
Any help appreciated.