The simple solution on any system with multiple problems evident...is to do a clean install.
By doing such, you at least remove the O/S and malware (to some extent) from the equation of what is wrong.
There are all kinds of reasons for system errors...with a bad hard drive not being the least of these.
If webpages are being redirected...that tends to point to the presence of malware.
Using registry cleaners...is a bad idea. It's a bad idea for many reasons...among them is the fact that system files may be removed by such...which are key to the proper functioning of the O/S.
Why I donít use registry cleaners - http://www.edbott.com/weblog/?p=643
Should I Use A Registry Cleaner - http://aumha.net/viewtopic.php?t=28099
In short...there are many reasons why your system is malfunctioning.
Since you can boot into XP and you have indications of malware...I am moving this thread to the Am I Infected forum (as a start), where the BC malware personnel can take a look at attempting to assist you. From this point on, take all instructions from appropriate members of the BC staff and please read/follow any administrative rules which may be posted in AII.