Problems with accounts and OS X Install Disc

Hi,

I recently discovered that somehow my account is no longer an administrator.
This means I can't install apps, updates, drivers etc.

I tried different things but nothing seemed to work. Then I tried to insert my Apple OS X install disc, that came with my Mac but when I put it in, the disc drive pushes it out again about 30 seconds later.. The same thing happens when I try to boot from it (by restarting and holding down "C"). So it means I can't boot from it...

The install disc looks good (no scrathes or fingerprints on it) and other CD/DVD's works perfect...

I searched the forums but i can't find anything.

- Rasmus

Need more info about your Mac and where you bought it and was it brand spanking ...

It's a white Macbook 2 Ghz, 1 Gb ram, 80GB harddrive. Bought it in april this year, and it was brand new.
It's got OS X 10.4.10 installed.