Try to disable your antivirus prior to opening a ms office file. See
if it takes so long even after disabling it. (note that windows
prefetch caches app files on a first run so that all consecutive runs
are faster).
Another thing I would advise you to do is to run a Disk Cleanup or
even better, download a free ccleaner utility from www.ccleaner.com
and run it to clean your system from unnecessary garbage.