This is not XP and we don't go on hunches here. There are Best Practices for which we set the standard for Windows 7 here, and there are Bad Practices which we help avoid.
To solve the Worst Practices you were following install Microsoft Security Essentials,
then enable Automatically deliver drivers via Windows Update (Step 3)
and run all Important And Optional Updates through reboots and completion. Keep Updates set to Automatic.
Most tech enthusiasts will not even run the corrupt factory pre-install with all of the bloatware lard and duplicate utilities that throttle Windows 7. They prefer to Clean Reinstall - Factory OEM Windows 7
following the steps to get and keep a perfect install. At the minimum I'd Clean Up Factory Bloatware
to turn off all the schmutz that's freeloading on Windows 7 largely to spy on you all day long.
In addition go over these Troubleshooting Steps for Windows 7
to assure all's well and learn a lot about your install.
All the best,
Microsoft MVP - Consumer, Expert