You should never have more then one anti virus program running in the background. I use a free anti virus called Microsoft Security Essentials, and I highly recommend it.
Another program I recommend is IObit Advanced SystemCare. It scans and repairs registry errors, defragments the registry, scans and fixs disk errors and more. Run a "Deep Care" scan with it.
You should delete junk files and old system restore points using Disk Cleanup, a program that came with windows.
Also defragment your hard drive using the program that comes with windows, just search in your start menu "disk defragmenter" and it will come up. I use Piriform Defragler (from the makers of CCleaner) to deframgent my hard drive because it shows more information, and it does a better job then the one that came with windows.
Make sure to download and install windows updates.
I recommend getting to Chrome, its probably the fastest web browser you can get. Or you can re-install your current browser to get a fresh start.
You can also re-install windows, but you will lose all your files though.
This should make your computer and internet faster.