First things to do: 1. Open Task Manager to see what is running 2. Run your anti virus and antispyware programs for a complete scan 3. Tell us what the "yellow light" indicates as most desktops have a green power light and a red drive light - or are you referring to the CD/DVD drive light? In the case of the latter being on check the drive has no disk in it.
Microsoft Lumia 950 vs Lumia 950 XL: What's the difference between Lumia 950 & 950 XL?