I been researching in upgrading my screen for my dell e5440 but i'd like a 1080 display. The 1080 display only came out for the e5450 which has 30pin connector and the e5440 has the 40 pin connect.
My question is can i still upgrade to the e5450 higher resolution screen if i get the 30pin cable?
No -- if the older system doesn't have the option of a higher resolution screen, it's not going to work with that screen.
There's more to it than simple physical connection - if the system doesn't have an entry in the BIOS table for the screen, you may see a screen that works only partially - or not at all.