Connecting MacBook to external monitor and peripheral devices used by a PC?
Depending on your PC specs you may use a VGA or HDMI USB KVM (Keyboard, Video, Mouse) switch.
This will allow you to connect 2 or more computers to one screen, mouse and keyboard, and switch between them pressing a button.
The keyboard and mouse must be USB (wired or wireless) in this case, so they work on both computers.

There are plenty on Amazon and eBay.

On my experience, VGA KVMs have problems with screen resolution and offer a generally crappy viewing experience; I ordered an HDMI one and may update the answer based on its performance.