Alt key misbehaving

windows 8.1. the alt key acts depressed every few minutes, when im not pressing it. malware checked multiple times, reboots, refresh, looked at sticky keys, no prevail. my virtual assistant does everything from turning on/off devices in the house, to managing emails and everything you can think of in between. keyboard shortcuts are a major part of the coding, and I must have normal use of the alt key. I have replaced the keyboard and it still exists. when it misbehaves, I can tap the key a couple times, then it is normal for a few minutes, then returns. how to fix this issue? HELP!