Appropriate permissions problem

[Jukeboxs]

I downloaded some Windows updates last night (XP Pro) and my PC suddently started acting odd. When I click on any shortcut or any other executible file, I receive the following error window with a red 'X' beside it: "Windows cannot access the specified device, path or file. You may not have the appropriate permissions to access the item." This basically paralyses me from doing anything on my PC (e.g. I can't open e-mails, open internet browser, open Microsoft Office, or uninstall anything).

The only thing I can remember doing after the updates downloaded and installed successfullly was click 'Deny' on a ZoneAlarm warning message advising that Windows was seeking permission to log my key strokes and did I wish to allow this. But, imho, I can't see how this would have caused my problem and so I think it is coincidence.

I have never had multiple users set up in XP (i.e. it simply logs on with administrator rights when the PC boots up), so I am confused as to why I am now experiencing problems with Windows security/permission rights.

I am at a loss on how to fix this, as I can do very little with these restrictions in place. I see my options as being:

i) Somehow fix this problem;
ii) Wind the system back 24 hours to before this problem first occured (assuming I have this facility active on my PC, not sure if I have);
iii) Copy my data onto my external HDs (assuming I am allowed to connect them), format my HD and reinstall Windows - hopefully I won't need this as i) or ii) should suffice.

Thanks for your advice!