advice requested: computer freezing up while using certain programs

So about a week ago after going to some random video site my computer started having issues with freezing up. it predominately happens when I launch firefox and I have noticed more issues when using sites like netflix or watching episodes of my favorite shows on nbc, abc etc etc but it does happen no matter what im doing while browsing. some times it happens immediately after launching the browser and other times it takes a few minutes.

Also of note: Sometimes I can get out of the browser and some times I cant. I also cant restart the normal way and program manager wont load and neither will any thing else. I have to completely turn off the computer. when it comes back on some times the sound icon on the tray at the bottom right will mention that it failed to load and will have a red x. Sometimes windows loads and looks like windows xp or before with strange outdated graphics. I have norton with latest definitions always installed and as far as I can tell there are no viruses or malware installed. Also for a bit Java kept saying there was an update to be installed but when I would click on the icon it would say that there was nothing to install. I eventually figured that out and as far as I can tell the latest version of java is installed. the last detail I can think of: after a hard restart yesterday windows updates where installed and then I noticed that program manager showed high CPU and physical memory usage was higher and when Ctrl+Alt+Delete is pressed for a bit nothing comes up and then the screen turns black followed by an error box pops up:"failed to display security and shut down options". I have started windows in safemode and ran a hard drive integrity check with nothing found. Im hoping for some direction on what I can do to try and solve what is going on. Im sorry for this long explantion but I wanted to give every detail I could think of.

I have norton through my comcast account and it continuously runs full scans that have not turned up anything. It does and has warned of blocked attacks from malicious code on some of the sites I have gone to.

Do check your hardware (temperatures, memtest), just as an easy option.
Also, full virus checks are better run from a separate system (e.g. liveusb) (just in case some rootkit managed to outdo the installed antivirus).
Also, there should be (somewhere) some recovery options for windows (i.e. to check for corrupt system files) which might help.