Components inside a tower-style computer case are largely exposed, and there is very little shielding to reduce the radio interference they produce. This is particularly true at the rear input/output panel of a PC. This is why cables that are designed to plug into the back of a computer often have a ferrite bead attached to them, to reduce radio interference. Also, the wireless signal weakens as it travels through the metal and plastic computer case and goes past the noise-producing components.
If you don’t have a port available on the front your PC, consider using a USB 2.0 hub to add ports located away from the back of your PC, or use a USB 2.0 extension cable to move the adapter to a location in line-of-sight with your receiving device.