This may or may not have anything to do with malware. Regardless, you can't very well work on resolving any malware issues unless you can get into Windows.
You did not mention your operating system, however, Vista will usually offer you an option to repair it when it gets into situations like you describe, so I'm presuming your OS is probably XP. Therefore, you should be able to use the Recovery Console if you have, or can borrow, an XP installation disk that is the same XP version as what you have installed, e.g., Home or Pro.
Change your boot options in the BIOS to allow your system to boot from CD, then, when offered, select the "Repair" option by depressing the "R" key. Once you have accessed the Recovery Console, enter the command, "chkdsk /r" (without the quotes) and then let it do its work. This process will most likely take several hours to complete. Just leave it alone until it has finished.
Here's a link to the Microsoft KB article on using the Recovery Console. To start the Recovery Console from a CD use the method described in option #2:http://support.microsoft.com/kb/314058
Hopefully, that will get you back up and running again. If you then feel you have malware issues, please come back, open a new topic, explain what problems you're experiencing, and include your HijackThis log.
If this doesn't get your system back up and running, then I would suggest you try a general troubleshooting forum, like those that can be found at the following sites:http://forums.whatthetech.com/forums.htmlhttp://www.techsupportforum.com/http://forums.pcpitstop.com
For a Dell computer, try here:http://en.community.dell.com/?~ck=ln&lnki=0&nav=true
If push comes to shove, you can always slave the drive to another computer so you can make a backup of your documents, pictures, etc. Then, reinstall the drive and do a clean installation of your operating system.