System Restore not working

Hi
Today, my PC (win XP) has been behaving strangely. First of all, I upgraded to IE7 as prompted by Microsoft Update. No problems here. Then Windows Defender prompted me to upgrade that one. I was running 1.1.1347.6, so deletd it then upgraded to the new Beta2.
When logging on to Internet, my screen freezes up in IE. I have deleted Defender now, but still problems of freezing. I am running NAV 2006, is this a problem at the same time as defender?
A month ago Chaslang sorted out a nasty malware problem for me and talked me through setting a System Restore point (thankfully), but I have now tried unsuccessfully to restore using the wizard on XP to go back a few weeks.
First point i tried was a Windows Defender Cheskpoint - unable to restore. Next poit tried Software Distribution Service 2.0 - unable to restore.
Any help here would be appreciated. I wanted to restore because i think it is a conflict here between recently upgraded programmes?
Can you spare the time to advise me?
Thanks
Steve

 

My system is MS Windows XP SP2, Intel Celeron CPU 3.06GHz, 1.0 GB Ram, Intel 82865G Graphic Controller. When all the above is going on and trying to get back to 'normallity' the PC's fan sounds like it is going to take off!
Internet ADSL 294.8 Kbps