Hello MG,

You tell us that you frequently "clean"you registry with different tools. Might well be in one of these cleaning sessions you lost some vital lines in the registry, causing one or more windows routine to search for a Dll or driver to load, but can't. Such problems are very difficult to recover from.

Personally I have some bad experience in the past and only do carefully cleaning if really necessary.

The best thing you can do now is backup all your data on your program/system disk and format and install your system (XP incl updates) and programs from scratch on. Avoid to install programs you don;t really need. Each program add's lots of data to the registry which becomes larger and makes your system slower.
De-installing routine of many programs do not effectively remove their entries.

I'm myself working with many programs, updating these regularly.
As average one per year I do a completely new system and programs installation to get back a fast running system.

Cheers Jaap