That's usually driver incompatibility with Windows 8.1 or more likely a faulty card or maybe antenna not properly connected to the 7260. Check and see if antennas are attached properly.
I've been connected for more than a day on my Windows 7 without issues as well as consistently getting my 100/10 internet plan all the time. I would try dual booting with Windows 7 clean install and if that still doesn't fix it, you have a faulty card or a faulty antenna hardware.
