Cant boot SAFE MODE after SP2 install

Normal boot to the Win-XP desktop works OK but I can no longer boot into Safe Mode. If I should encounter a problem in Normal Boot, then I’m in big trouble with no options to fix it.

This happened just after installing SP2 which I would like to keep as I like the new features.

I’m guessing that some required drivers is not being loaded during a Safe Mode boot. Any suggestions on how to troubleshoot or fix this would be much appreciated.