Sounds like your laser is dirty:
First thing you need to do is crack her open, unplug the dvd and hdd drives and remove them.
Leave the hdd in it's tray thing for safety ann unclip the dvd from its tray. Unscrew the dvd and clean the lens - should solve the problem unless the lens is actually dying in which case you've got a few options...
Have a read around here and on the forums to get a better idea of what you'll need to do - but here's a hint:
replace the dvd drive
or
forget about it and just transfer stuff via ftp (
{X3} requires
{X3} modification
{X3} of
{X3} one
{X3} form
{X3} or
{X3} another - it's up to you to decide which one ::cough::
{X3} ::cough::

Seriously though have a read on the forums (these ones or
http://forums.xbox-scene.com) to decide which chip will be best for your needs!