I switched on my computer but i get the following message on booting
hard diskette seek failure
keyboard failure
invalid configuration information.

i try to press f2 to get into the bios but nothing happens.
i replaced the bios battery with a new one but still the same problem. My computer is a dell dimension E521.

Contact Dell tech support. Even if your PC is out of warranty, they will still talk to you and try to help. You just won't get any free, replacement parts.

Ditto what CimmerianX said. Dell has very good tech support, and you can chat online with their tech people. They are better even than my own company's help desk people! If you need a repair, it will be reasonably priced. If it is something that should not have happened, they sometimes replace/repair parts out-of-warranty, especially if it is not too far out... :-)