hit CNTRL + ALT + DEL to bring up taskmanager.
click on the processes tab at the top.
look down the CPU list and see what is using the most CPU
and let me know what the SYSTEM IDLE figure is.
what are the specs on the computer, RAM, PROCESSOR ETC.

also :-

Go to Start | Run
type or copy the following:

regsvr32 urlmon.dll .then click OK.

Do the same with these files. Go to Start | Run Type in the following one at a time. Then click ok.
regsvr32 Shdocvw.dll
regsvr32 Msjava.dll
regsvr32 Actxprxy.dll
regsvr32 Oleaut32.dll
regsvr32 Mshtml.dll
regsvr32 Browseui.dll
regsvr32 Shell32.dll

let me know if any don't register.