Thanks for letting us know about this issue, and I'll try to help figure out what's happening here.
First of all, are you running Intel GPA on a single system, or in a dual-system (client/server) mode? Also, which tools are you running when the problem occurs -- just GPA Monitor, or System Analyzer or Frame Analyzer as well? If you "disable instumentation", do the keys start working again, or do you need to do a reboot? Also, are any anti-virus software programs running on your system?
Also, you might want to try right-clicking the GPA Monitor and changing the default capture key through the "preferences" option, as the default capture key may be conflicting with another application you have running.
And last but not least, please include of copy of the output from running "gpa_system_inspector.exe" from the GPA install area, as this will help us understand your specific configuration.
Thanks in advance for your help in gathering this additional information as we work to resolve this issue.