One of my servers OS kernel messed up the other day.
One of the techs fixed it, but ever since I haven't been able to gain root access.

I've never had to do this before and I don't feel like bothering the techs... but I'm sure you can, well at least I think you can... I saw it in the Linux documentation somewhere... but do you think I can find it? Nope! Well, okay, I skimmed through it, so here goes...

How does admin change the root password?

Well apart from the usual "it's linux, just use a root exploit to get a uid 0 shell and then run passwd", the solution is to boot in single-user mode (ie, boot and press a key (can't remember which) before it finishes booting) and then you can reset the root password.

But yeah, you need console access, so unless you've got a remote serial console attached (eg, a modem + phone line hooked up to a com port) you'll have to bother the techs.

err... darn!

Sorry, should of specified. Yes, I'll be doing this task remotely (without a console).

I suspected that was the case.

You know, it is quite likely that the tech who fixed your kernel also reset your root password. They should have told you if they were doing that of course, but they might have forgotten. In any case repairing a broken kernel is pretty similar to reseting a root password, in that they both require console access and (usually) booting into single-user mode.