Windows 7 Intermittent Windows Explorer Not Responding.

My problem may be the same as a lot of others that I've seen reported but here is my version. After booting I move the cursor to the 'Start' button and the hour glass appears. After several clicks I get the message "Windows Explorer is not responding" followed by another message about problem determination. I then get a message about restarting Windows Explorer. I restart it and all is well. The only activity that I could identify was Avast had just finished updating. This problem is very intermittent. This is a clean install of W7 Pro 64 with all current maintenance. Hardware is a Thinkpad T500 with all the relevant Lenovo specific drivers. I am the only active user on the machine. This system has been running since early January. The problem started about 2 weeks ago and has occurred 4 or 5 times. I boot every day and most days there are multiple boots. No changes (that I'm aware of) to the configuration. Anyone got any ideas or opinions. TIA for your help.
Bob Helms

Disable Avast loading on startup (msconfig => startup), to see if it's causing the error.

cybercore said:

Disable Avast loading on startup (msconfig => startup), to see if it's causing the error.

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Didn't make any difference. Had 1 occurrence Wednesday. This time I told the system to shutdown Windows Explorer. Everything returned to normal as if nothing ever happened. I read somewhere that corrupt files my contribute to this problem. Does W7 have a way to seek out and correct/fix corrupt files? Thanks.
Bob Helms

I've upgraded to Avast 5.0 Free. I've also turned off the automatic updates. The "not responding" issue hasn't happened in over a week after turning off the automatic updates. I'll post again if my issue re-occurs.
Bob Helms