Lack of night time erection points to vascular or neurogenic cause. Check TSH and testosterone level ( < 300 is low) Screen for DM: glucose, A1c, lipids Exam: breast for gynecomastia ( elevated prolactin), testes for mass and penis for plaque. Nocturnal Penile Tumenscence to r/o organic cause, US of penile arteries to r/o obstruction.