Before calling for help, try this:
- Close all programs, if possible.
- Shutdown your computer, if possible.
- Turn off the power to your computer, if possible.
- Unplug your computer's power cord from the wall socket.
- If a laptop, remove its battery.
- Wait at least 20 seconds.
- If a laptop, reinstall its battery.
- Plug the AC power cord back into the wall socket.
- Switch on the computer.
- See if the problem returns.
Why does this sometimes work?
Microprocessors (CPUs), when programmed perfectly, execute only the instructions that their programmers intend for them to execute. Sometimes, when confronted with unexpected inputs, a CPU will execute unexpected instructions. When the CPU encounters an undefined instruction, it will halt. When this happens, the computer seems to freeze or "hang up". The only way to correct this is to reset the CPU.
Many computers contain more than one CPU. Modern power supplies don't always turn off all DC power to all CPUs. The only way to ensure that all CPUs are reset is to remove AC power from the power supply.
That's what you did: you forced a reset of all CPUs. Congratulations!