When I had my prostatectomy the urologist cut and capped a main vein is that prt of y I can't get an erection along with nerve damage since blood?

Nerves alone. Damage to the nerves during prostatectomy is enough to cause ed. See your urologist to discuss options.
Please seek 2nd opin. This is a complex matter far beyond the limitations of a q&a forum. Schedule a second opinion with a specialist.
See a urologist. Post prostatectomy erectile dysfunction is treatable. An evaluation by a urologist may determine the reasons, talk to you about chances for recovery and also and more importantly give you treatment options.