Blank page after creating account

I just re-installed the cart the other day because I tried to add a mod and the whole cart went kaput! Now, it is not working again. When I create an account and press the submit button the screen goes blank. The account is created, but you'd never know! It happened after I changed the registration email. So, when I uploaded an unchanged file to the server again, there was no change. Then I uploaded the whole cart again hoping all the problems would disappear, no luck. I cannot for the life of me figure it out. I've done searches on here to find out what I can do, but have had no luck. I've uploaded the debug mod, but again, the instructions are not clear about where to find the error logs.

Also, after I changed the email message I got the header errors too! I tried the admin login and got the errors, deleted the two extra lines that the page pointed to. Does anyone know about these two extra lines and why they create a problem?

I am hopeless. We were supposed to go live this weekend...there are lots of people waiting to register for the conference...

wbwg.org/registration

Thanks for any help. I'm lost, I can't tell you all that I've done in my effort to fix the problem...

Thank you MickYelta for your help. :bigups:
Not being totally confident about the errors I found, the problem was the extra two lines that were created after ?> (the PHP closeout) on the on the install of the shopping cart, mostly in the includes>languages files. What a great relief to have this figured out, and what fun it is to learn about PHP.