iMac G5 Superdrive Problem

Hi there: I have an iMac G5 20" which I bought in May 2005. I use Mac OS X 10.4.7. The machine has been generally fine and have been able to burn CD's/DVD's etc. fine. Last weekend while trying to burn a CD - I put in a Verbatim CD-RW formatted disc (as that was new and unused) and the iMac Superdrive spat it out. Since then, the iMac seems to be rejecting all my CD's/DVD's by spitting it out after few minutes of whirring and reading. Now, I can't read any CD including the iMac start up CD.

My Superdrive details are as follows:

PIONEER DVD-RW DVR-K04L:

Model: PIONEER DVD-RW DVR-K04L
Revision: D441
Detachable Drive: No
Protocol: ATAPI
Unit Number: 0
Socket Type: Internal

PIONEER DVD-RW DVR-K04L:

Firmware Revision: D441
Interconnect: ATAPI
Burn Support: Yes (Apple Shipped/Supported)
Cache: 2000 KB
Reads DVD: Yes
CD-Write: -R, -RW
DVD-Write: -R, -RW, +R, +RW, +R DL
Burn Underrun Protection CD: Yes
Burn Underrun Protection DVD: Yes
Write Strategies: CD-TAO, CD-SAO, CD-Raw, DVD-DAO
Media: No

Any leads would be greatly welcome and appreciated.