I'm having the exact same problem.  I'm an experienced sim pilot and used to FMC/CDU programming, IRS alignment is fine and all required data is being entered into the CDU but nothing is working??  When I engage LNAV or VNAV - no response at all.  If I engage heading select, it does not respond and the climb rate window remains blank all of the time when trying to select a manual climb rate.  Very frustrating - I've read the manuals more than I care to mention and at the moment stuck for ideas as to what to try next!!!