Why does the Mac not go into recovery mode (cmd + r) and disk manager (alt)?

Question

macOS

Hello!
Faced with the need to reinstall the system cleanly on the 2007 mac pro desktop, but problems arose:
1) it does not enter recovery mode (cmd + r), simply not responding to keystrokes, it loads the system as if nothing had happened.
2) and when you try to select the boot mode from a USB flash drive (the option button at startup), it just hangs on a black screen, the power button on the monitor blinks.
What could be the problem?
UPD
First of all, I thought about the keyboard, checked it, it is fully working, besides, on the wire, native Makov's keyboard with num block of numbers.
Of all the possible key combinations, only safe mode (shift) and memory reset (cmd + alt + p + r) work.
Haven't tried hard disk mode(T), boot from cd-dvd(C), command line mode(cmd+s).
The rest either do not respond and immediately launch the system to the desktop, or launch the system to the user selection screen.
Bootloader selection mode (Alt) no matter how you hold down this button (when rebooting, after rebooting or turning on, when turning on, etc.) a consistently black monitor screen and a blinking button on the monitor itself.
By the way, I forgot to write such a fact that when you turn on the computer, the screen shows absolutely nothing until the desktop is loaded.