Please test yout PC keyboards in ZX emulator. Searches for the appropriate keyboard for real ZX Spectrum / ZX emulator.
This is keyboard tester:
On screen show active keys. You must test all this keys combintions.
All three pressed keys must by signed on screen. If any of this keys combinations work incorrect(any key is ignored), then your PC keyboard is not useful for using with emulator or connect to real ZX(with PC keyboard interface). Please inform me about error signed combinations and write type of tested PC keyboard.
(my old PC keyboard CHICONY with microswitch key buttons work absolutly perfect with all this combinations , only cursor keys+0 is impossible use )