Uninstall, install from the original disk and update to the version you need. But that does not help you, on the contrary, it will not give you all the bug fixes that 5.03 gives you and MB Looks normally works without problems with 5.03, so better check you have the latest Looks version.
Deinstall MB Quick Looks and install it again.
Thanks for your replies. Turns out it wasn't the Premiere Pro update which caused MBQL to hang, it was my graphics card drivers which were also updated at the same time. I restored my PC to an earlier configuration and re-installed 5.0.3 and everything works fine.
Congratulations on your success, and thanks for reporting what your issue was, and what got it fixed for you. If you do not mind, what was the video driver, that gave you issues? That'll give us all something to think about, when a similar problem arises.