"Cannot Run Two Device Installations"

I can't install any new hardware on my Win XP Home PC. Getting above message saying:

"You can install only one device at a time, when it is finished you can try this wizard again".

I wouldn't call this neither wizard nor "plug and play" system.

I am definitely not doing two installations, just powering up PC and trying to install a new printer! I tryed all ideas I could find on the net - none did help! Try cleaning junk files, registry etc. I desparately need help.

Thanks, MP