Macbook Air has problem reading external HD

Hi,

I have noticed the same issue on two Mac laptops that I have owned recently, one is Macbook Pro 13" which I replaced recently with a Macbook Air 13", the problem is that both have a serious problem reading external HD which is formatted as FAT 32. The HD blinks for a while then stopes blinking without the system being able to detect it (sometimes is does but rarely and for a short time then it disappears).

I know that the usual explanation is that there is an issue with the HD or that to assume that I am doing something wrong (which is typical support way of doing things), so I shall explain more:

- It is on USB 3 and I am using the same cable and tried all USB ports

- It was formatted from my Macbook Pro as FAT 32 so I can use it for windows as well

- It worked perfectly for some time but then stopped

- Both Macbook Pro and Air are on Yosemite and faced exact same behavior

- Most important issue is that it works perfectly every time on my Windows laptop (so obviously the problem is with Mac)

- The name of the HD is PQI i think it is a Chinese manufacturer and it is 500GB

Hoping this is taken seriously and the soonest.

Regards,

Tawfik