explorer.exe keeps on vanishing.?

im using windows xp. Explorer.exe keeps on vanishing and appearing. so im unable to work with desktop or any other folder.
ive symantec updated in my system but it finds no virus. ive spyware doctor and it also finds no spy.
pls help me.
ive also used sfc/scannow. it copied essential files to dllcache folder but the problem still exists.

Try to replace it by downloading the latest or the existed version:

http://www.microsoft.com/windows/ie/ie6/downloads/critical/ie6sp1/default.mspx

CD full of new and useful software

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