Just got my 10 inch Mb quart sub installed with my rockford Fosgate amp... all of a sudden the bass stops and i don't hear it anymore, I'm running the stock amp with a Hi/lo Convertor i checked the fuse in the battery its still good also checked the amp the light is still on

 

You can check to see if the amp/sub work by connecting an RCA to 3.5mm adaper cable like this --> http://ecx.images-amazon.com/images/...L._AA1500_.jpg and playing audio - if the amp/sub play then you know its an issue with the hi/low convertor.

Is the amp power light on?
Is the amp protect light on?
If you press on the sub cone does it depress?
Have any wires worked themselves loose? Touching eachother or anything they shouldnt?

Realistically though.. the easiest (and most direct fix) is going to be taking it back to the installer. Its probably best to do that before disconnecting or working on the system since you risk the installer not buying the 'it just stopped working' story if you've dismanted everything trying to fix it yourself.