Excel Locked for Editing - Locker on "C" Drive

I just got a new laptop w/ Windows Vista. My old laptop is Windows XP. I did occasionally experience LFE (Locked for Editing) on XP but it cleared up after I exited excel. The LFE problem w/ Vista is very severe. I've shut down & rebooted several times but could not clear up the LFE. I cleared up the temporary folder but that did not help. I even copied the sheets to a new file w/ a new name, but that did not help, either. However, if I copied the file on a flashdrive, then it worked perfectly. It seems that something in my new laptop detects the content of the excel file on Drive C & locks it up. If I open the file fm flashdrive, then it works fine maybe because the "locker" on C drive cannot reach it on the flashdrive. Would greatly appreciate any advice on this.