It sounds like you have an awful lot of corruption in your profile already.
best solution: wipe the machine clean, erase/format the hard disk, and return everything to factory new.
install the programs you need, (remove any you don't need) and get all the updates.
install & run antivirus, then move all your data back from your backups.
not-so-great: it may just be a bad user profile.
create another user, log in as that user. See if that other user has as many troubles.
if not.. or at least if less.. then copy/move all your files from your old profile to the new user you created. (everything under /users/yourname in Win7 - including hidden & system files)
that should get most stuff to work, and put all your data where you need it.
In any case - all this corruption means that there is already a problem on your hard disk. the kinds of programs you are downloading are more likely than average to have viruses.
this stuff could be happening because the machine is overheating (check airflow, clear any dustbunnies)..
or from electrical problems (brownouts -low voltage as well as lightning and high-voltage spikes)
.. or old age on your hard disk.
* 3 years begins old age on an average consumer hard drive.
If you cannot pin down a cause, then it could be some combination (viruses)(heat)(age)(electrical flutter) , and possibly user mistakes. - forcing a shut down will also damage your hard disk.
good luck!