Logining in

Question

i have been on facebook for a little over 3 months and all of a sudden last week when i tried to login i get the message that my e-mail is not registered. however, i am still getting friend requests and messages to that e-mail and i can not get logged in. my profile is still up.....any suggestions????? i have e-mailed them numerous times in the last week and have got no resolution. please help!