The game is susceptible to save game damage when the PC crashes. Long term you should think about doing backups of your save game.
Short term you can try to substitute the originals with the corresponding .bak files in your current save game. In your case that would probably be players/********.ttp (if you lost stuff in your inventory) and vehicles.dat (for the vehicles obviously).
If that doesn't help, just click F1, enter "cm" and use the new tab (called Creative Menue) to regain the lost items and vehicles.