White and laggy screen

Hi all,

I have a MacBook Air (13-inch, Mid 2011, 1.7GHz, Intel Core i5, Intel Graphics 3000 384 MB) running El Capitan (10.11.2).

The problem is that after a few months without turning it on, when I did it, the screen seemed to have a white overlay. After a few days, the white intensified and the refresh rate seemed to become slower and slower. Also, when I move the mouse or type something, the previous positions of the cursor is still displayed, like a trace of the movement, then it fades after a few seconds without moving the mouse. This problem also occurs when booting in safe mode.

When I plug in any external display I can see that the machine works fine, so I just turn the laptop screen off and just use the display.

Trying to fix the issue, I ran all sorts of diagnostics and/or processes I could find in this form (reseting PRAM and SMC, Apple Hardware Test (AHT) and others, such as OnyX), to no avail.

The AHT returned with no issues found, so I'm hoping it's not a hardware issue.

There is no genius bar where I live and authorized tech support costs 250,00 just for diagnostics and if any work needs to be done, they tell me it may cost up to 3k, so I'd really like to avoid that.

Is there a definite way to rule out hardware issue and, if so, to find which driver or other issue may be malfunctioning? I really miss using my laptop as a laptop, instead of a desktop 😟

Thanks in advance for any help you may provide!