How was Win7 activated?
Did you reinstall with just the OS DVD, or Recovery?
If you clean reinstalled did you keep the Dell Utility partition?
Has the problem been there since the reinstall or did it possibly begin after your changed out a driver given by the installer or optional Windows Updates?
Run a virus scan with Malwarebytes and MSE, which is a better free AV solution than Avira.
Google repeat errors in Event Viewer>Admin VIew and Performance Diagnostics log at Control Panel\All Control Panel Items\Performance Information and Tools\Advanced Tools where you can also Generate a System Health Report.
Try a clean boot procedure: How to Troubleshoot a Problem by Performing a Clean Startup in Windows 7 or Vista
Uncheck all items at msconfig>Startup except AV and gadgets.
Run chkdsk and maker's HD diag/repair full CD scan: Hard Drive Diagnostics Tools and Utilities (Storage) - TACKtech Corp.
Run sfc /scannow to make sure nothing has already corrupted System Files.
Finally, if nothing else helps then run a Repair Install
which is next best thing to reinstall.