There is at least Control Panel\All Control Panel Items\Administrative Tools\Event Viewer. Also, it's possible to check Blue Screens, but you haven't mentioned any --- hardly the problem.
Avast could be the fault, especially if you have several different security programs running, they may collide. Why not try to disable
all security programs, and test run a pdf program? With Windows 7 updated, you can stay for a few hours on Internet without really risking anything.
Also, it could be a Registry problem. I'm not so wise with those, I can only recommend what I've been using,
Free Window Registry Repair: a windows registry repair freeware., it's worked well for several years BUT many experts suggest that you don't use these "simple programs". IF YOU DO, be sure to have it create a System Restore Point, that way you can return if something goes wrong.
An extra issue could be, kind of connected to the Registry, flaws in uninstall. A rather known tool is Revo,
Download Revo Uninstaller Freeware - Free and Full Download - Uninstall software, remove programs, solve uninstall problems, it presumable cleans your computer better, I actually liked it as much as to by the pro version.
To find out what your computer has fed on may be just as difficult as to find out what your dog has fed on. A zillion things going on in a computer during a single day. And it's not necessarily software, it may be hardware. Anyone with warranty, not having a clue, I always recommend to contact a professional service. It's safe, sure, and it also gives a livelihood for the pros, thus securing we have the service tomorrow too.
Best of all.