Prevent duplicate entry in userform

i want to
(1) Prevent duplicate number in ACCESSION NUMBER FIELD

(2) If someone not writes ACCESSION NUMBER FIELD prevent from submiting....

I SEARCHED A LOG BUT NOT WORKING I FOUND ONLY DUPLICATE ENTRY DELETE CODE..

thanks in advance

wowwwwwwwwwwwwwwwwww

GENIUS MEN ))))))))))))))))) tehneXus BRO u r genius u coded so fast i have replaced accession number with textbox7 so i made changes and it worked very nice both queries solved ... i am a data entry operator u helped me lot may god bless u