My shift key stops working after a few seconds?
First, make sure Sticky Keys are disabled as it can cause potential issues with gameplay (hitting shift 5 times can trigger the prompt). Second, consider using a wired keyboard if you've been using a wireless one previously. Some wireless keyboards (typically the low-end generic ones) may only acknowledge a key press for a couple of seconds as a power-saving measure. Many of the well-known manufacturers (like Logitech) are power-efficient enough (lasting for a minimum of 3 months, but can be rated to run for 3 years on a fresh set of batteries). Third, double-check the keyboard specs. Many "typical" keyboards use dome switches, which are fairly cheap to produce & have more limited number of simultaneous key presses (typically maxing out around 4 keys). Mechanical & gaming-geared keyboards tend to use more expensive components to improve tactile feel & tends to have higher simultaneous key press counts (typically around 10 keys, but may go higher). If you hit such a limit, the oldest keystroke gets dropped for the next key. Finally, if the keyboard is a bit old or used, you might want to open it up & double-check the internals as the connection for that key might be worn, off-set or dirty. If the key is worn & using a mechanical standard (like Cherry MX, for example), you could just replace the worn key cap. Dome cap keyboards don't have this option, so if a dome of worn, all you can do is just replace the entire keyboard. While this might not fully remedy the issue, I hope this gives you some ideas to help troubleshoot your issue.
New World Man
Sounds like the switch is just not getting pushed properly (tends to happen as keys get used, they were out a bit). What I have done in the past, can take some playing around with to get the right length - but pry off the key (CAREFULLY - they may be a metal bar on it, you'll want to so how it is attached) there should be a hollow tube that pushes the actual switch. just stick something in that tube so it makes better contact with the switch. I have used all kinds of things for this, but the two that have given me the best resaults have been cutting a small piece off the tube that holds the ink on a pen, and - bevieve it or not - a dry cannabis stem.
Uncheck where it says Turn on Sticky Keys and click OK. If this doesn't work try checking the keyboard language if set correctly. - Go back to Control Panel then look for Region and Language and make sure all tabs at set to the United States. - Click Apply when a change is made then try your keyboard again