Combo drive gone crazily slow

For the last couple of days my Lite-On combo drive is performing too slowly. A 700 MB cd takes 12-15 minutes to write. I haven't installed any new software other than games. I use Nero 7 Premium. One more peculiar thing is that it takes lesser time when writing at 40x than 48x and 52x. The CD-DVD drive speed test utility gives a average writing speed of 7.22x when settings are set for 40x. 6.65x when set for 48x and 6.95x when set for 52x. please help.