Back to them to correct your new PC and get it working.
bought a new pc, first thing i did was update the drivers(gtx-750ti) then unplugged computer hdmi and re-connected XB1 hdmi. bout an hour later i got off xbox, plugged my pc back into my monitor but it won't re-connect for some reason. just says no hdmi input will auto shutdown in 5 mins. Also bought a vga and that gives the same message. The monitor is a Dell S2415H