The issue is diabetes mellitus (DM) and erectile dysfunction. Diabetes is a common cause of impotence but this problem usually comes when the disease is for a long duration and one has complications and blood glucose is not under control. In your case, it does not seem to be related to DM. Most likely its due to psychological factors. Another factor may be tenormin, which is a beta blocker and is known to cause erectile dysfunction.
My suggestion is that stop tenormin and if need be, switch over to some other antihypertensive medication. I think you can use Viagra/Cialis safely, if you do not have an underlying heart problem. Meet a physician for the prescription.