How can I fix this?

The Short Story
After make a modification to paypalwpp.php and then putting the original file back because the modification produced errors, the Paypal Express Checkout module no longer shows up--like it was never there. IPN still works fine.

The Long Story

I made a modification to the paypalwpp.php file in the includes/languages/english/modules/payment folder. I gave me a parsing syntax error or something so I put the original file back.

I got the same error but on line 1 this time.

Then tried restoring from yesterday's backup. Then I got a completely different error along the lines of a payment.php (I think that was the name) was trying call a nonexistant function or module.

I overwrote the restored paypalwpp file with the original copy I made before doing the modification.

Payments then went through OK but noticed that Express Check out module does not show up either on the admin or customer side. Only Paypal IPN is displayed. That's the one I want to use anyway but I at least want to fix whatever is wrong.

Can you help? Praying this is easy to fix. Thank you.