This was tested on a Steam copy...download the DX10 EXE;
Run it with compatibility mode OFF. If you have the CTD when creating a profile, make sure your Windows "Saved Games" folder is on YOUR C DRIVE. It HAS to be in the default C:\Users\XXX\ directory.
Run it, create an account - for me, this made my multi work in DX10...so then I tried it in DX9 (performs better), and whoosh, it works!
I also did find that under my saved games folder, in my profiles folder, a new ini file had been created called "outline.ini". Inside it are:
login = 'YourLogin'
cdKey = 'YourKey'
password = 'YourPass'
So you can also try simply opening Notepad, copy/pasting that in, and replacing everything with your info (the key is stored as XXX-XXX-XXX, with the dashes). Save it in your HAWX/profiles directory. Lastly, make sure that the '' are in there.
Good luck, post here if it works for you.
Are you able to get into coop campaign games?