Dell Dimension E310 Desktop freezing?

I had reinstalled the OS [XP Pro] on this unit a few months ago, now the owner says when they go to the net, it's taking forever for pages to load but each time I start, first, after the windows screen, it is taking like a minute or two before going to the desktop and when it does get to the desktop it's tkaing like 5-10 minutes for the desktop to load. Also, it's trying to connect to the net but doesn't so I can't run an online scan, I tried installing MBAM both in SAFE and regular modes but it does not install.

This desktop has Norton on it, I did a Norton scan, turned up empty, I am thinking of doing a repair install first but decided to check here first if there's anything else I can try?

 

Ok, let me just ask this and I can start doing the repair install and then reload OS if needed, since the Norton AV program is not reporting any viruses then is it safe to say this is NOT a virus problem or since MBAM won't install is it safe to say that it IS a virus problem just that Norton is not detecting it?