Some serious prob with Liteon DVDRW

my comp specs are:
core2duo 1.8
2 gb ram
asus p5b
liteon 20X

the prob is since yesterday i m not able to use the drive.
wherever it plays any cd or dvd.. the comp almost freezes.. and the transfer rate has also gone low..
while watching movies from drive the sound also flickers.
can anybody suggest wat may be the problem