Ok. Have you done the following? (follow to the letter!!)
Install M2TW. Install the patch 1.2 (make sure it matches the same language version as your original) do the same for patch 1.3 (choosing the wrong lang version can mess up your installation).
THen download and run BC from here:
http://www.twcenter.net/forums/showthread.php?t=140857
make sure you select the right language version when prompted.
if you have vista, make sure to download the VISTA FIX from the same post on the above thread.
Then download and apply patch 1.05 here:
http://www.twcenter.net/forums/showthread.php?t=142288
there are another 4 fixes in this thread. I recommend applying them too (if your not sure about how to apply them then just ask)
I also recommend one final defrag before running the game (it certainly makes BC run quicker for me)
If you have and the game is still not working i recommend a full clean install (it seems to do the trick for most people). Unistall M2TW and then go into C/Program Files/Sega and delete the sega folder. Then type "regedit" into search/run and delete any entries which have "Sega/M2TW" under the software headings (delete your save games too!). Then i recommend a defrag.
This clears any remnants from your pc. Then do the above starting with installing M2TW. If this is too laborious, try reinstalling BC. If it doesnt help do a fresh clean install of everything.