Any M.S. Project masters out there?

MS Project is driving me nuts.  It's not properly updating resource costs for me.  If you have a resources budget at say $100/hr, working a standard 40 hour week for say 12 weeks the cost should be $48K (40hr/week x $100/hr x 12 weeks).  If I then change the resource usage from 100% to 50% that should drop the total to $24k.  Sometimes it works, sometimes it doesn't and it's driving me nuts.  After making the update I will go back in and see yes, the usage is now 50%, but the total is still stuck at $48k.

Any idea what's wrong and how to force recalculations?  thx.

Note.  It's not always on updates, sometimes it doesn't calculate correctly right from the start as well.  I found this when my boss sent me a rough and ready outline that I started refining.  I noticed that some of his inputs weren't giving the correct answer so I started updating.  After no luck I deleted all resources and started over.  That fixed it at first, but then when I started tweaking things up and down it wasn't properly updating again.

Frustrating.  

P.S. YEs this is a legal version through work with all updates, I'm not working opn some broken down third hand pirated copy.  And no, another program isn't the answer either.  This is a corporate IT decision and we need to share with customers / suppliers.

Uh oh. I was just about to install it myself. Maybe I'll keep using Excel

Just want to be sure that when you say "started over," you mean from a new file, yes?

Have you re-installed the app?

I'm not a Project power user, but I've gotten some pretty good help on MS's own help forums -- may be worth asking there?

You might also try https://www.msofficeforums.com/

That said, I don't know how good the Project sub-forum is; there are some super-helpful people there for writing macros for other MS apps, however, so maybe some similarly sharp Project users there??

I used it extensively earlier in my career on smaller projects, where P3 was over-kill, but now the Project Controls folks on my teams do everything in P6.  Its been some time but I'm assuming it's like riding a bike.  I'd vote the issue is how the individual Tasks are constrained.  I'll draft a more complete answer when I break down and open the work laptop back up and can pull up MS Project.  

Is the file proprietary, or it is something you can email me to take a quick look at?