On the face of it, you have one PC in which software that looks for certain settings like date is using a 'local service' branch of the registry, rather than the 'user' branch. Somehow the local service value for 'short date' has been changed, but you dont see the change in most running software because you run them under the 'user'. settings.
I would suggest signing on to the highest level of user 'administrator' in safe mode, and setting the short date as you want it. Thats a guess based two facts (a) that Access is probably old software from win95/98 days and knows nothing about 'system' and 'user' settings (b) I just changed my short date setting from dd/mm/yyyy to dd/mm/yy and lo! the event log display changed, so that proves where the event log setting comes from....
PS I just realised it is more complicated than that - under C:\documents and settings, there are ntuser.dat files (registry??) for no less than (a) default user (b) local service (c) network service (d) your user name, but NOT for (e) all users. When I made the change I just described, (b)(c) and (d) versions of ntuser.dat changed, but not (a).
