Put The HARD Back In Hard-on !
Your state of mind can have a big impact on your ability to get aroused. Even if you're with someone who you find sexually appealing, worrying about whether you'll be able to please your partner can make it impossible for you to do just that. One of the effects of the stress hormones is to narrow blood vessels. When less blood flows into your penis, it's more difficult to get and maintain an erection.
Your erection - or lack of one - can actually alert you to underlying medical problems throughout your body. Conditions like high blood pressure and high cholesterol can damage your blood vessels, impeding blood flow to your penis.
Please do the RIGHT thing and consult a medical practitioner first.