Came back from a week away to find my 250W DE light stopped lighting up in my absence. My tank is esconsed in darkness.

Apparently it worked fine on Saturday, but on Sunday wouldn't light up. I played around with it a little today and indeed, can't get it to light.
Can someone lend me a 250W light to help me diagnose the problem? I suspect it is the bulb but before I order a replacement, I should confirm that the ballast is working OK.
Ideally, someone could lend me a spare bulb for a couple of days, but failing that, if someone had a bulb that I could just use to test fire the ballast for a few minutes, that would work too. Please let me know ASAP if you can help out, I'm desperate!
Thanks!