Hmm, try removing the dock program first of all.
With a problem like yours, is a task of finidng out the culprit one by one.
To delete the program if you can't, go to Safe Mode, by pressing (should be F8 at bootup), and a menu will come up to select Safe Mode.
Choose Without Networking, since firewalls don't tend to boot up when Safe modes on.
If you don't have enough hard drive space, this may be the case. I'd search for programs within Safe Mode you don't need.
If you've never used it before, it may look slightly strange, since sometimes the resoloution is wrong, etc, but ti stops many programs running that could stop the computer booting, etc.
I hope this helps.