Question : XP SP3 PROBLEM

I recently installed SP3 for XP, which installed OK. However, my machine will not boot up into Normal Mode.  It goes through the POST, then windows starts to boot, but after a very few seconds it shuts down and starts again, taking to the Boot up Options screen.  It willl start OK in SAFE mode, but not NORMAL.  

Not sure why this is happening.  I suspect SP3 may have detected a Virus or some such, but why did it install OK ?

I've tried using Autoruns to disable drivers, and CCleaner to fix 'Issues', but still the same.

I have AVG Free, and NO Adware running.

I have backed up all the Data files, and do have a full [ and I assume clean] backup from Disk Image taken about 2 weeks ago., but I'd prefer to solve the current problem if possible.  And presumably if it can boot into safe mode, it must be basically OK.....or not ?

Another option is to wipe the drive, and start again, and restore the data files at the end.....but re-installing all the Prog files, such as Pinnacle Studio 12 would be a real pain !

So any ideas please ?

Answer : XP SP3 PROBLEM

Trust me Rod, if you've backed your important data, do a fresh install, don't waste time on detection of this problem. You'll loose more than with diagnostics than with clean reinstall.

With the new installation, please don't use AVG, as I had lousy experiences with it as it tend to report non-existing viruses.

If you do a clean install, please download Microsoft Security Essentials which is also free and surely work better.

And if you still want to detect the possible issue, for a start I would remove all traces of AVG and CCleaner.

Also, you may wan to try to download Dr.Web CD and boot from it, do a full scan of your PC and report back.
http://www.freedrweb.com/livecd/