what do you mean the dvr show unavailable? You can get to on demand though? Before the tech left your house everything should have been working and he should have given you an oveview of how to use everything. When you press the my dvr button what happens, when you press record what happens. are you sure you got a dvr box?
you still have not said if you are talking about mydvr manager or your physical cable box. If its the box unplug it and plug it back in, if that doesn't work call your local office and tell them to look up your account to make sure you have the dvr registered to your account.