I have been taking norvasc for approx. 1 year and am not able to maintain an erection for any length

Unfortunately sexual dysfunction is a reported side effect of both Norvasc and Diovan HCT (although considered rare.)
http://www.drugs.com/sfx/norvasc-side-effects.html
http://www.drugs.com/sfx/diovan-hct-side-effects.html

Diovan contains a combination of two drugs, hydrochlorothiazide (a thiazide diuretic which can cause impotence problems) and valsartan (an angiotensin receptor blocker much less likely to cause impotence).

Every drug affects each individual differently so it might take some trial and error to find the right treatment for you.

from http://www.drugs.com/enc/drugs-that-may-cause-impotence.html

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If you think that a medication you are taking is having a negative effect on sexual performance, discuss the matter with your health care provider. NEVER stop taking any medication without first consulting your health care provider.

Among the anti-hypertensive medications, thiazides are the most common cause of ED, followed by beta-blockers. Alpha-blockers are, in general, less likely to cause this problem.