For anyone considering uninstalling AVG and moving to another AV (I'm a very happy and un-stressed Avast user)
this uninstaller, from the AVG site, could be a must.
Uninstall in the normal fashion, then run the appropriate tool, (there's one for 32bit, the second for 64) and a reboot somewhere during this process might be indicated.
AVG also installs a BHO, Linkscanner I believe it's called, that may need to be uninstalled separately. Altogether it has become quite a bloated bit of kit, from many accounts. And the protection/removal of the free version might leave something to be desired.
(Avast, on the other hand, boasts the same detection/removal in the free and the pro. Just don't expect to be able to schedule a scan, or automatically handle actions if anything is found during a scan.)
Frankly, having used Avast for a couple of years, if I missed the features unavailable in the free version, I'd be quite happy to purchase the pro. I think it's as good as any of them, and better than a lot. (They could be a bit more pro-active at adding malware definitions at times, for some malicious files.)
There will be a new version af Avast out in a month or two. Version 5. I think the current version will remain supported for a few more months after that. (If anyone is really interested I can try and find out.)
PS, mostly, it is not possible to have more than one AV installed, even if one is disabled or inactive. Full removal, using the appropriate tool if available, is necessary in most cases, before installing another one.
(Naturally, all required packages should be downloaded first, then the uninstalling done offline.)
Failure to do so can result in all sorts of hiccups, quite often a while after installation, and it is possible that the OP might be as a result of this.
New machines often ship with all sorts of bundled crap. Not all of it uninstalls cleanly.