System Resore Java Error?

This is a bit of a sprawling issue, so I hope I've hit the preferred forum.
For the last 2-3 weeks I have had problems getting Windows XP to recognise both my MP3 interface and that of my digital camera.
I could manually locate my digital camera, via My Computer - assigned as the F drive, but my MP3 was not recognised at all.
Using advice from a forum, it was suggested that a System Restore might be the first place to look.
I confess that I hadn't tried that because a previous attempt was rewarded with a message saying that Windows was not able to do that.
At that point I turned it off in disgust.
However, I guess that this action had purged the restore data held at that point, replenished the disk space available and got it working again, because it worked and both pieces of hardware were recognised again.
So far, so good.
Later that day I revisited the Secunia website for an on-line scan to check that all my major programs had been restored as current as possible with regard to security issues.
Despite having gone there with no problems over the last 6 weeks or so, the scan could not take place owing to the site's inability to load the required Java applet (the site told me this).
I imagined at that point that that this problem was down to my Java having been restored to an earlier version by System Restore and that some vital element to that had been junked by either Registry Mechanic or CCleaner during one of my registry clean-ups in between time.
No problem, I thought, just un-install it then re-install Java from the Sun website.
But no - Windows Installer came back with the message "The feature you are trying to use is on a network resource that is unavailable".
I am aware that there are a couple of elements to Java, but have regretably not got round to getting properly informed about their function within the Windows (XP Home, Service Pack 3 in my case).
So far, I haven't missed whatever it does in its entire form, but I have noticed a few blank spaces in some websites and I cannot use UK websites to make purchases that require the "Verified by Visa" additional security layer.
Any assistance with restoring Java fuctions to the usual would be much appreciated. I have visited the Sun website and tried a couple of downloads, but both were met with the same response by Windows Installer.
I am also not really keen to go for a further System Restore as not only did my Kaspersky Internet Security 2009 complain bitterly with messages about corrupt files and vital security data being compromised, but I couldn't say at what restore point I would be resurrecting the problem at the root of it all.