I had this happen to me, and it was VERY aggravating. I knew that I could do it, but I would just stop running!!
What I finally had to do was run up and jump on the springboard, and do a straight jump to a mat, then a taller mat. Then I ran and did a straight jump to the table. I did front handsprings and flysprings on the tumble trak and the trampoline.
I would but a block at the end of the tramp, and then bounce up to it and do front handsprings and half-ons over it.
After a while, I put the mini-trampoline board in front of the table, and ran up and did the smallest little handstand on the table. It took a long time to even keep running, but once I got the little handstand, it got easier. If you can't do that, shorten your run, even to just a few steps. I think that the root of my problem was that my steps were always messed up about a foot.
Keep doing the handstands until they get higher and higher, and start to make your run a few steps longer. After awhile, you will get it, so don't stress out so much. Once you get the fhs vault back, slowly introduce the other vaults.
If you have any videos of yourself vaulting watch them, or just picture yourself doing it. You can also watch videos on youtube of vaults.
I wish you the best of luck, I know how frustrating mental blocks can be!