I installed sp2 and some programs don`t run

I installed SP2 into an inspiron 2650 and some problems began!!!

 

The laptop now is slower than before, but the biggest problem is that I CAN`T open any windows aplications programs (like control panel, windows explorer...).

 

When I click the application I need to run, the cursor stays quiet for a while and then disapears all the desktop icons for a moment, then appears again and sometimes appears that "drwtsn32.exe found a problem and must close".

 

Some aplications I have been installed run OK!.

 

The problems began after I installed SP2.

 

Could someone help me?

(I have XP home edition installed in my laptop.  I downloaded the SP2, I didn`t installed it from a CD)

 

Thanks.