system
6
If you HAD some security program, ever, you need to run the respective removal utility. A program not being active (or having been uninstalled already) doesn’t mean it can’t have some conflict with avast.
Since you are suspecting from Avast being the source of the problem, maybe you should run its removal utility under Windows Safe Mode and then manually clean up any remnant folder. Then install the latest stable version and reboot.
OTOH, it may just be some other thing altogether, like some defrag needed or a hardware problem in your HDD (just to give some examples of possibilities; I don’t have any indication whatsoever, so please don’t take this as any kind of fact or real conclusion).