I usually run prime95 and furmark for 4-6 hours to stress the cpu and gpu first. Keeping a close eye on it for the first 30 min. If it passes, then ill run prime95 for 24hrs. Running stress tests also gives you an idea how good your cooling is. I've never gone higher than 61 degrees on the CPU and GPU.
I agree with sunder, test the USBs and all the ports and check error logs. I had a USB not recognize one of my USB 3.0 flash drives, but it recognises my other USB 3.0 flash drives. The flash drive that would work in the USB 3.0 port worked on my laptop's USB 3.0 ports and all USB 2.0s. It was weird. It turned out to be a drive.