For the definitions of those terms I'll point you to
www.wikipedia.org , there you'll find much more stuff than the one I can provide you here
For the problem in video playback after your PC reformat, the problem lays most probably in the codecs used to decode your movies...
Read
BSPeter's "READ THIS FIRST BEFORE POSTING" post (especially items 3 and 4).
Use GSpot to know which codecs you need for which movie, and then install them (you can install FFDShow for almost everything, and nowadays its performance is comparable to the other wellknown codecs such as XviD, DivX, etc.)
If you'll have still problems, tell us which filters are used by BSplayer when decoding movies (righ-click -> Options -> Filters -> Advanced), and the type of video you want to play (extension and GSpot information)