Problems Opening ALL Programs After Renewal

Hello- so very recently I've been experiencing some problems following my renewal of a subscription of Norton Internet Security. I realized I had to renew this after I found a Trojan of some kind on my computer. The virus was so intense that I couldn't access the internet in any way, but I managed to renew, do a complete scan and get rid of the virus. Anyway, now I've been experiencing a bunch of problems with my computer and I'm not sure if they are due to the virus or Norton. I can't launch programs at all by simply clicking on the icon anymore- I'll be forever caught in a weird circular game of "choose the program you want to open this file" (which is weird when it's internet explorer and the option is internet explorer) and it never works. I can resolve the issue by right clicking "run as administrator" but this doesn't fix the problem. Another sign that there is something wrong is that I can't run dxdiag on my computer- when I clicked on the icon (despite having downloaded it multiple times) it says that it failed to launch.

 

Anyone have any idea as to what is going on here?

 

Oh, and if it helps, I use Windows 7 on an HP.

 

Thank you so much,

 

Katie