I decided to rebuild my work PC, and install XPSP2 RC2 on it.
That all went well etc etc installed a few other apps, rebooted it today though and I lost my startbar.
So i messed round with a few things, deleted profile, tried a repair with no luck.
Then I rebuilt and installed XP SP2 again, with no other apps this time though, and bugger me it happens again. After a SP2 install and reboot the startbar is missing.
Perhaps it didnt like the permissions I set on something...
Ah well, rebuild no 3 on Monday.

