text being "eaten up"

[stellbread]

I am revising a document, hit one key and get multiple characters )for instance if I type an "r" I get 3 or 4 r's), then the program begins deleting everything after the last letter I typed, doing so at high speed. I have to disconnect my computer, reopen the file and then I find myself back at the ;last place I saved. The rest of the text in present, but I have to go back and revise a couple of pages I had already edited. This is puzzling. I've been to repair shops and showed them this via video and they are perplexed. 

[#2]

Does the issue only affect one document, or can it be replicated on multiple documents. If it is only one document, if you upload a copy of it, one of use may be able to see what is causing the problem.

If the problem affects multiple documents, there may be a fault with the keyboard that you are using. Can you try another one?

[#3]

@Doug_Robbins_Word_MVP 

I've changed keyboards, mouses, moved it away from other electronic devices, have taken it to computer repair shops and the workers there are perplexed.