Lightroom 3-W7 64 bit won't work
From your description, it sounds like LR is crashing on startup. You could check to see if there is a newer version, even a minor update, beyond your 3.x version. If yes then install it.
Or you can try repairing the current installation (run setup again and select Repair if given the option), or you can try uninstalling LR3 completely (delete all preferences if given the option), reboot and reinstall from scratch.
This is just generic advice that would apply to any application crashing immediately upon startup as LR appears to do on your computer.