You can only run one resident AV. You'll need to totally remove what you currently have before you can install a replacement.
The easiest thing to do is to do a clean install of Avast:
Repair Avast:
Control Panel> Program and Features (Add/remove program)>Select Avast> Select Repair. Reboot when completed
https://www.avast.com/faq.php?article=AVKB204
If Repair doesn't fix the problem, try the following:
Clean Install of Avast:
https://goo.gl/4Ptzkf
Thank you for your reply, Bob.
Doesn't the Repair option just reset things to original and fix anything that may have become corrupted?
Also, as I stated above since my Avast protection has now expired so would it even do anything at all?
ETA: I have tried to uninstall/reinstall but am unable to as for some reason I do not have Administrator authority even though I was set up as Administrator and the only user on this computer and I am still showing as such under User Accounts. Someone told me that they thought Microsoft changed something when they stopped supporting Windows XP SP3.