RE: dell latitude E5440 dark screen?
I'd suggest a clean install of Windows 7 and all drivers, if that's what you want. It doesn't sound like a hardware issue.
You may want to seriously reconsider the Air -- a Macbook Pro might be a suitable replacement for your system, but the Air is a tablet with a keyboard - it's not the workhorse your current system (or the Pro) is. The Air is also a dying lineup - it hasn't been updated much in several years (the CPU is three generations out of date).