Way too many to have one solution for you, but what I usually do when all else fails is use a Boot-Time Scan! Avast has one in the free version...
This is the second post I've made about a Boot-Time Scan in 5 minutes..... Oops
When all else fails for me I use a boot-time scan... Seems to do the trick when I have any issues that seem impossible to resolve.
I believe Avast antivirus offers a boot-time scan even in the free version!