If you have been using the computer successfully, with an earlier OS, it is unlikely to be a hardware fault. There are two culprits in the devices, which might be causing it. Open the Device manager and navigate , first to the Network adapters. Right click and select your adapter from a list, should there be one. Right click it and the select properties and the Power management tab. In the window, untick the item "Allow this device to turn off the computer to save power". As you are using a second monitor, possibly this is on a USB outlet? Scroll further down to the "Human interface Devices" and carry out the same procedure.