Thank you for the info about warranties, but I still have the other problem . Can anyone give me any idea what the cause might be, please?

The problem is,  I can be in the middle of typing a word when the blinking cursor (which is usually at the end of the last letter you've typed) just disappears and anything else I'm typing doesn't appear on the screen. I have to left click at the end of the last bit of the typing that did make it onto the screen, and retype what's missing. This happens every few words and is very annoying.It isn't any particular letter, just seems to be random.