G'day chretien,
Damn, that's some problem you got there........
Short of Uninstalling NFSHP2 for the moment .......
Delete your desktop shortcut to BF1942 & go to your bf1942 directory & find the "BF1942.exe" file. Right click this & select > create shortcut. Drag it to your desktop & double click that shortcut to start the game........ Does that work...?
If not it sounds as though maybe NFSHP2 & BF1942 files are mixed up in the same directory....Which is possible if your not careful given both game folders default by install in a EA Games folder.
A quick simple solution if that didnt work would be to Uninstall NFSHP2 completley from your machine..... try to run Battlefield 1942 & if all is okay install NFSHP2 again....
Goodluck......
Let us know if that worked......