NES game pad has it’s own connector that doesn’t for in to any PC socket. In case you still would like to play PC games with it without breaking then try building simple USB-NES controller adapter. Cool part with this is that adapter can be unplugged any time if you would like get back to console.
USB adapter is based on Attiny85 microcontroller running V-USB stack. All it does – reads NES controller commands and sends them to PC. Adapter uses USB HID class, so no drivers are needed. Once plugged in it appears in game controllers list. Tested with Win7 and Ubuntu.