Win 7 C: drive missing folders starting with 0-9 or letters A-E on reboot!

Brand new computer running Windows 7. Copying folders from external drive onto C: drive (root directory). Seems ok but on restart/reboot any folder that started with a number or the letters A, B, C, D, E are gone e.g. Bills, 1AXA Data etc. Similarly, if I went to create a folder that started with the above I had the same problem. Never had a problem like this with XP, 98 etc. Rang computer shop. Answer was - why are you trying to save in c:, just save in My Documents. Now this has appeared to work satisfactorily but hardly resolves the problem. Any assistance would be appreciated.

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