Explorer.exe 25% - cannot access folders

After startup computer runs fine then suddenly access to files and programs stops. Have narrowed it to explorer.exe which runs at 25% when it should be idle. Sometimes it happens quite quickly and sometimes after more than an hour.

Logging off and logging back on cures the problem until it happens again but ending Explorer.exe in Task Manager and running it again doesn't help. This happens on both accounts on the computer.

Have run full scans with Macafee have restored the computer back as far as I can and reinstalled updates; RegCurePro doesn't seem to find anything either. I have also reinstalled my browser: Chrome

Have seen other similar posts - one referred to ini files which I didn't try but can't find it now.

A couple of months ago I had the "Your Windows is not genuine" problem but that seemed to vanish after a time.

Seen several posts with similar problems but 'solutions' don't seem to work.

Thanks if you can help

My windows is genuine - it was preinstalled on the computer purchased. I assumed it was a virus scam and that my anti-virus had dealt with it.

Thanks for that. I have always resisted these 'cure' programs before but a solution for the "Windows is not genuine" problem suggested it. Probably from the publishers!!!! I was stupidly misled by the "Microsoft Partner" description!!!
I'll have a go.