Faliure in the First

I didn't buy this one, my customer did it, so I set it up with best of my knowlege.
Got DHCP address from modem and working fine and dandy. Then he called the internet light keep going out and need to reset the modem and router to get it back and only last about 1hr then problem come back again.
I thought it was my problem so I went back and changed out the modem and bam less then 1hr he called back with same problem again. Turn out that it had a bad firmware from factory, I told him I don't support it, so he upgraded the firmware him self and still having problem, but now its in 1 or 2 days instead of 1 or 2 hours.