Screen saver temporarily freezes computer

I recently upgraded from Vista Ultimate 64 to Windows 7 Ultimate 64.  Ever since that time, whenever I activate the screen saver it temporarily freezes the computer.  The longer the screen saver is running, the longer it takes to go back into the desktop after I click the screen saver.  If I click it within a few minutes after it goes into screen saver mode, no problem.  If I wait for an hour, it takes about 1-2 minutes.  If I wait overnight - it could take 5-7 minutes.  Moreover, if I require a password/ log-on screen, the delay first occurs after I log back on and manifests itself as a blue screen (that is, when I wait to click the screen saver within an hour or so); if I have the screen saver on for a long time, and then i click the screen saver , the screen saver itself freezes for a while (5-7 min), then the log-on screen appears and once I log on, there is no additional delay.  If I turn off the screen saver and just run the lock mode, there is no delay.

I tried Dell's tech support, including the for-pay option, and they have not been able to solve the problem.