Check optional Windows Updates for newer drivers. Look in your Device manager to see if any drivers are in error, update or change them.
Study the Event Viewer>Custom>Admin View to google repeat errors to learn about them and how others have resolved them.
Check also the Performance log on Advanced Tools page accessed by clicking your WEI score at Computer>Properties link. Look for cued issues at top of Tools Page, Generate A System Health Report.
Type "solutions" in start search box, see if any Solutions have been sent to problems reported or not.
Test your RAM using memtest86 CD for 5-6 passes, or overnight to really stress test it.
Test your HD using maker's full diag/Repair CD scan: Hard Drive Diagnostics Tools and Utilities (Storage) - TACKtech Corp.
followed by Disk Check
Is this a clean install or a factory install of how many years? Consider a Repair Install
as a last resort before a Clean Reinstall which is better than getting a new computer - some tips on getting a perfect install based on hundreds I've done are here: re-install windows 7