[CentOS] CentOS-7 problem

I installed CentOS-7 on an HP MicroServer from a KDELiveCD (on a USB stick), and it ran OK for a couple of days; but yesterday it wouldn't reboot - the dots went round the circle indefinitely, and when I clicked on Ctrl-Alt-Delete it said "[OK] Reached target Initrd Default Target". There didn't seem to be any way to reboot except to press the power button.

I tried running the rescue kernel, but that didn't help.

I tried installing the netinstall iso on a USB stick, and choosing the repair option - this ran ok, and I was able to run grub2-install, but this failed to boot as before.

I'm wondering if there is anything else I could do to resuscitate the system?

Fortunately, I kept the old 6.5 system in another partition, which I am using now.