various programs wont install or update - XP

Hi, I hope someone can help. This problem has been going on for a couple of months and is afecting more and more programs.
I'm running XP, service pack 3, all updates are installed.

This is what been happening:
Tried to run iTunes, (it had run ok previously, no recent updates) iTunes wouldn't start.
Tried to download and reinstall iTunes - wouldn't work
Followed Apple's instructions to remove all apple apps including Quicktime and reinstll - still no install

Spybot won't update, when I hit the update button - nothing!

I use Microsoft Money 2000. Has been working fine for years, now when I download a statement from my bank it does not automatically import into money like it used to.

Am unable to access Device Drivers in Control Panel - I get a permissions error even though I am Admin

There are a few more things like this of apps no longer running or behaving correctly.
I have Avira AntiVir running but it finds nothing even on a deep scan. I have used Spyware Blaster, IObit Malware Fighter and Advanced System Care 4 nothing is found.

I am a retired PL/SQL, Java developer so I know my way around a pc. I do have Hijack this installed.

Any suggestions please.
Thanks for your help

 

Probably best to do the R&R to ensure it's malware free and get some logs. Read it through carefully before beginning the process, run the diags sequentially in the given order, make notes of any errors.

 

OK, I went through the R&R as instructed and so far its all looking good. I have managed to get iTunes to install and Microsoft Money to behave.

Thanks to all for the R&R postings and keep up the good work, I really appreciate it.

 

I'm pleased to read you're making progress