ughaibu: Is it just not brainking you are having problems with ?

If it is everything then it is a problem lol. Is your computer old ?

Is there any chance of doing a System Restore ?

If you have re-installed Firefox AND still having problems logging here, or getting on the web i doubt it is Firefox. East thing to do as Rose say is try another Browser (preferably no IE lol). Chrome is a good choice.

If it is still problems with the web, it is either your connection or the pc. Connection you would have to talk to your provider providing you are sure your end is set up correctly.

PC problems could be endless, if it was ok, and now it is not, then it is case of finding out what. Which is a process of Elimination. IF you have no System Restore point all you can try is the things you should run regually anyway.
First thing to do is make sure all your virus protection is up 2 date, and run that. Run which ever system cleaner you use. Run Scan Disk. Run a Registry cleaner (Eusing do a good FREE one). Lastly Defrag it.

If you had some sort of error message it would be useful