Q I installed OpenSUSE on to a PC that had been fine with Windows, including browsing the web. With OpenSUSE it was also able to browse web, but on reverting to Windows, there was no LAN light on the modem-router (a TalkTalk-supplied Huawei SmartAX MT882). I uninstalled the Windows driver and re-installed, with no improvement. Multiple complete shut-downs and re-starts made no impact. Reversion to the previous day's restore point made no impact. Restarting OpenSUSE again made the LAN light come up and browsing was OK, but this didn't help the situation in Windows. Deeply disenchanted, I switched the power off at the wall and went to bed. This morning I fired up the PC in Windows, and the LAN light is back, with all seeming OK. Can you advise what was wrong and what may have changed to resolve it? I have no idea if the issue lies in the PC or the modem-router but I hate 'miracle cures'.
A The problem lies in the PC, and more specifically in the way that Windows initialises the network controller. When you start the computer from cold, the device is in its default state and Windows has no trouble initialising it. When you reboot Windows, things still work, because the driver expects the device to be in the state it left it before the boot. The problem arises when you boot from Windows to Linux. Windows sees this as a warm boot, but the card has not been initialised in the way it expects, because the Linux driver was handling it last.
These problems are usually caused by drivers uploading specific firmware to the card - it is possible that the Windows and Linux drivers use different firmware versions, or simply the Linux driver leaving registers set in a way that confuses the Windows driver. Either way, the simplest solution is to shut down the computer instead of rebooting when you want to switch from Linux to Windows. A simple Shutdown from the desktop menu followed by a press of the powerbutton may suffice for this. However, as the motherboard still receives some power after a shutdown, you may find you have to switch off the power at the wall socket or the switch on the back of the PSU for a few seconds to ensure a fully cold restart. This would explain it working again when you switched on the next morning.