First cleanup your startup software, remove anything that is unrecognized, unrelated to OS or running Apps., then look at Services and Hide Microsoft, this will show which services were installed by software, disable the ones that do not belong anywhere.
Get CCLEANER from FILEHIPPO and run a registry scan.
If no fix, insert XP install CD and Add Software, go through the list and let it install.
Or open command prompt and type: sfc /scannow. That will scan and fix damaged windows files. I would run a virus/malware scan first.