To fix this problem, you have to put exact path to PowerShell by following next steps:

1. Click on "File" in PyCharm
2. Choose "Settings..."
3. Open the "Tools" branch
4. Choose "Terminal" in the dropped down list
5. In "Shell Path", change powershell.exe to

"C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe"

PowerShell destination may vary between the Windows versions. So, in case that didn't work, try to find the powershell.exe manually in your Windows folder.

If it's possible for you to operate with cmd, instead of powershell, you can complete next steps:

1. Click on "File" in PyCharm
2. Choose "Settings..."
3. Open the "Tools" branch
4. Choose "Terminal" in the dropped down list
5. Change powershell.exe to cmd.exe in "Shell Path"
6. Click on "Apply"

In case you still have problems, make sure that "Include system environment variables" is enabled in the right most part of the "Environment variables" bar.

That solution applies only if cmd.exe is enough to launch and operate the tasks you need to accomplish.