About 40% of the time, when I type a t, a new window opens an my cursor is there. I have to click back on my original document. If it (just happened) opens a browser window, I have to close that. It started in Win 7 and carried over to Win 10. How do I st (and again) op it.
It could be a bad key on your keyboard. If you have a desktop PC, try another external usb keyboard. Does the t still fail?
If you have a laptop, disable the internal keyboard and plug in an external usb keyboard? Does the t still fail?
If the t works on the 2nd keyboard on the desktop PC; you've got a broken t key on the original keyboard and it should be replaced.
If the t works on the external usb keyboard on the laptop, the t key is broken on the internal laptop keyboard and that should be replaced.
If the problem persists with external keyboard on either the desktop PC or the laptop, you could have failed hardware and you need to test it. It could also be Windows corruption which would require windows repair/reset/reinstallation. Also, you need to scan for virus/malware infection. Use your built-in AV scanner and scan/remove any viruses found. Retest. If no viruses/malware are found, go to Malwarebytes.org and download free Malwarebytes antispyware program and scan/remove any spyware viruses found.