Q: Problem with external monitor

Hello, I have bought a Mini DisplayPort to VGA Adapter from Apple recently and it has worked fine for a couple hours. I had trouble getting it to work at first but all of a sudden the monitor was recognized by the Mac, which at first wouldn't recognize the monitor. Then, my Mac went to sleep and the monitor was never recognized again. I would need help to make it work again as I don't know how I did to make it work in the first place.

I have a mid 2012 Macbook Air (June) with 128Gb of SSD, 4 GB of ram and 1600 Mhz DDR3 as well a 1.8 Ghz Intel Core i5 processor and the adapter (MDP to VGA) is brand new. It has worked, so no hardware issue, my monitor works fine, I have tried reseting PRAM AND SMC along with booting in safe mode, nothing worked. Anyway, I hope you guys have an idea of what's going on, so thanks in advance!