my computer takes ages to perform a simple task and more often than not does not respond can any one please help .ive defraged ,on broadband but no joy all this started when i lost system restore which ive only just got back thanks to you.but going back dosent solve the problem

Here is a good guide from owen:

Cleaning Up and Speeding Up

You might also want to consider posting a HijackThis log in the Spyware Section:

please follow owen's Instructions and then post your log in the Spyware, Adware, Viruses and HijackThis Logs section (Not Here).

Hope this helps.