I’ve seen this a couple of times now. After uninstalling Oracle XE the Windows 7 eventlog service stops (Windows Event Log). Before anyone blames Oracle alone on this I’ve found similar posts with the same issue on installing/deinstalling Sql Server.
Here’s the best fix I’ve found, and I’m posting this as much for myself as anyone else:
Hope this helps.
The main issue I’ve found was correct by changing the permissions on the folder and items in the folder %WINDIR%\system32\winevt\Logs.