A few comments... Spybot is worthless, in my opinion, for finding any serious threats... and RegClean doesn't work properly in Windows XP... though it was terrific in W98, WME, and is useful for some specific tasks in WXP... but it is not a good registry cleaner and has not been updated since 2001 or 2002 as far as I know.
You might install that hard drive in an external USB housing and see if you can rescue all your data...
Because it appears to be that you will need to reformat the drive to get it to work properly with Windows XP, VISTA, or 7 until you do.
Using an external USB drive housing will allow you to recover all data... but if you need to save your email and internet files, you will need to know where they are stored... or use a paid recovery software tool to rescue them.
Your problem could easily be a hard ware problem, or an spyware infestation... but since you cannot run Avira or Avast in current mode, or Windows Defender, Spy Sweeper, Spyware Doctor, SuperAntiSpyware, Malwarebytes, you are not going to have luck finding some evil spyware.
