I installed 64bit jessie on a new HDD, and initially used the 3.16.0
kernel. Then I installed the 4.50 kernel and ran into trouble.

  kernel:[25090.816205] NMI watchdog: BUG: soft lockup - CPU #7
      stuck for 22!s
        [colord-sane:20969]

This message is displayed every few seconds in whatever happens to have
the focus and is accompanied with a beep. The keyboard and mouse
hang so that I must do a hot reboot.

Is this in fact a kernel bug?

How (simply) do you tell GRUB to boot an earlier available kernel?

Is there any reason not to purge Grub and install LILO in place of it?
Grub is too difficult for me.

Haines Brown