Windows 7 boot manager error message

When i bought my Dell Inspiron 1545 it had windows vista installed in it , but when windows 7 became avaliable i got the free upgrade to install windows 7....I'm not sure if i did something wrong, but when i start my computer a window pops up (windows boot manager) and it asks me to choose an operating system...There are two choices, both being windows 7....Only one of the choices is a working operating system though...Does anyone know how i can get rid of this windows boot manager pop up and make my computer start correctly and load my windows 7 operating system like it should?...I would appreciate any help....

                                                                                                                                                                                            Thanks, Paul