Why does not enter the BootROM menu, Huawei switch?

Question

Windows

switch huawei, when you reboot there you can press ctrl + b to fail in the bootrom menu. and so it does not work, at least press down. greeting writes they say press, a two-second countdown leads.
upd.
I connect via serial port using putty v. 0.7. There are a lot of these switches, all the other variables are the same, some of the switches are normal, now these two have come across, it doesn’t work on both.