On many keyboards, PrtSc shares a key with SysRq. In the early 80s, IBM designed this key to allow users to switch between operating systems instantly. It was intended to be a "boss key" on a system level. However, the software support for this never materialized.
Despite its utility, the dedicated key is slowly fading into obsolescence, replaced by more sophisticated tools.
Check if you have an "F-Lock" key enabled on your keyboard, or try using the Fn modifier.