From little knowledge and lack of sympathy with games I would uninstall Theme hospital.
Then if the game was installed less than 5 days ago boot up pressing F8, choose Command Prompt only.
Then type " scanreg /restore " and follow the prompts, choosing a date before the game was installed.
If that is all too negative, and you don't mind a spot of fiddling, have a look at Autoexec.bat and type " rem " followed by one space in front of any lines that refer to your game.
Also look (via msconfig) in the startup list and un-tick any lines which load your game.