I never replied in this thread for the cause and the fix - I was having voltage drop-outs in the power circuit (Freezer, washing m/c, drier all on same circuit as Wx PC, 100m cable to house from pillar box, 2 phase supply).
Apparently the usb was going ding-dong - off - and then re-instating with Dong-Ding - I only learned this once I fitted speakers to the PC!! Sometimes this would happen inside 2 secs - Off and then On again. So Windy setabout checking in the WDWebcamCapture software for re-instating a link to a camera when signal or connection was lost and this has fixed the problem for my No2 Camera. I didn't need to replace the camera after all!!
Sorry, this will not be your problem Windy, but thought others may need to know what was my problem and how you fixed it.
TK