LOTS OF POSSIBLE REASON'S FOR THIS.
Do a Full Low Level Format first.
If you recovery CD is an original by the the notebook manufacturer, Use it to do a complete reinstall.But go to the manufacturers website to look up possible solutions concerning your model.Sometimes certain PC or laptop do not upgrade correctly.The manufacturer does however offer certain solutions.Check ther first.
SP2 has always been a bit touchy with drivers.
make a list of all the drivers u need and go the manufacturers website for eachdriver brand to get updated drivers for SP2.Ex: Nvidea,Intel, Realtek,C-media.Etc..
Install those prior to sp2.
download the sp2 pack from microsoft,the one the mentions f(for IT administrators).Uninstall all antivirus.Big problems can accure if you don't . restart
then install sp2.
give it time ,even if it takes more then 10 minutes.
If after 20 minutes still no response,well you have a problem that only a pro can fix.

If you do not know how to do any of this, you should not be trying to fix it in the first place!!
You have already done what you can. Let a pro handle it.