ah, well was going to post, but while composing my reply there were a few good answers, so i won't bother with my full blurb. an invalid link path or registry run item path can cause this, amongst other errors. sometimes these oddities are hard to trace.
if you still have the problem, look for the entry that has the same initial path, ie. if your unwanted opening folder is "C:\Program Files\Microsoft Office", look for the startup item in msconfig or regedit's "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" items, in my example, "C:\Program Files\Microsoft Office\" Office12\winword.exe would match, the quote in the wrong place would cause the folder to open rather than word.