font problems

[Angela Partain]

Hello,
My problem has gone from bad to worse!   I now realize that since I purchased the Y&Y Upgrade, I have been unable to typeset symbols that I was previously able to typeset.  They show up as blank spaces or Courier, so I have probably turned in several papers with incorrect symbols!  For example, I always type a \square after each Proof, and now it's leaving a blank there. 

I purchased the MathTime version of Y&Y, not the CM version.  Does MathTime not include many of the symbols such as \square, \leqslant, (the list goes on and on of all the symbols I am unable to use)?  Or did I do something wrong in the installation?  Do I need to purchase additional fonts to be able to type calligraphic letters or the \mathbb (or \Bbb) fonts?   The most puzzling thing about this is that I was able to use most (or all) of the symbols before (not the calligraphic letters, however), but now I am not. 

Your assistance is very appreciated.
Best,
Angela