HijackThis is not a tool which should be used without complete understanding. Fixing the wrong thing with it can cause troubles for a system, as you've found out.
There is a restore function in HijackThis, but even that is not always successful in returning things to a previous state, as some files get deleted.
Some applications may need to be reinstalled, a repair of the operating system may be required.
- Open HijackThis and click on View the list of Backups.
- Check each item showing you need to restore and then click Restore
- Click Yes.
- Reboot your system.
If you're still having troubles, and you think you're infected, follow the instructions in this thread:
http://www.techsupportforum.com/f112/if-you-think-your-computer-is-infected-203704.html
Otherwise, seek assistance in the MS Computing section of the forums.
