if your keurig will work with just hot water but will not work with a k cup inserted, the issue is the exit needle on the bottom. I just racked my brain for 3 days with this issue. i took the entire machine apart and then put it back together with no resolution. Wasn't until I put a paper clip thru the bottom needle that everything went back to normal....thank baby Jesus!
The reason the keurig was shutting off with a k cup inserted is because the water would enter the k cup but couldn't drain thru the bottom so all the grounds and water would back up into the top needle this causing the keurig to off (safety feature)
If you have this issue and this fixes it, let me know!