Intermittent lines in monitor from one laptop but not other

[wutang112878]

I have an HP W20171d monitor which has worked fine for months now and I have 2 laptops connected to it via a KVM switch.  Today it began having shaky lines in it from one PC, but when I switch over to the other laptop it was fine.  Then the lines went away when it was hooked up to the troublesome laptop, then they came back, then they went away again.  This laptop is also hooked up using a HDMI to VGA convertor.
 
Any ideas on what this could be?  I rebooted and there were some windows updates and a video card driver update installed but the intermittent problem still happened after that.  Any clue on what I should be looking at?

 

[cromulence]

A connection somewhere is probably loose or decaying, whether it be the KVM itself or the cable between the monitor and the KVM (since it's happening with all the devices, or at least I think it is). Try bypassing the KVM entirely and see what you get.

 

[wutang112878]

Didnt think of bypassing the KVM, good idea.  It isnt happening with both devices though, one works fine but the other had the intermittent issue

 

[Harry Hooper]

You could also try swapping the two laptops on the KVM switch and see if the problem "migrates" to the previously non-troublesome laptop.

 

[cromulence]

Oh OK I get it now. Yeah, also do the above if it goes away without the KVM. It's either the cable or the port on the KVM (try switching ports if you have free ones). If it doesn't go away without the KVM, it's probably the VGA/HDMI out on the laptop.