Hi, Russell - good to hear from you, and apologies for the delay in getting back.
To answer your questions:
Yes, the Dell laptop is dropping its connections, whether wireless or wired to the Zyxel.
Dell went through a lot of checks in Device manager, and numerous ipconfig interrogations. /release and /renew appears to restore the wired connection intermittently.
I've tried the Dell laptop on both an (Old) Netgear WG602 and a (new) TP-Link WA701ND, and basically the same problem, though there's no pattern of faults that I can see - it's just unreliable.
We tend to use Chrome 30 whenever possible, though we have IE10 as a backup on each machine.
Enabled add-ons in IE are Adobe: Shockwave Flash and a load of PDF items; MS - Win Media Player, Silverlight, Live ID Sign In, Office Doc cache; Trend Micro (anti-virus); Atheros CIE Speech BHO Class.
No, Dell tech support has not tried a reset to default of the IE settings.
In addition to the Dell laptop, on the same desk I have a Dell desktop, also running Win 7, and also capable of wireless and wired connection. There are no problems with this machine.
We also have a Dell Colour Laser on the network, and that appears to disconnect itself regularly.
All these problems seem to have arisen with changing to the Zyxel router, which we installed recently to cure problems with accessing our WiFi with Apple and Kindle devices. The previous (ancient) router wouldn't allow us to download anything to Apple and/or Kindle, and that problem is now solved with the Zyxel.
I am back online at 1815 GMT - 2000 GMT Monday, and then from 0800 GMT Tuesday.
Many thanks, XXXXX XXXXX look forward to hearing from you.
Thank you for your suggestion, Russell, to turn the laptop Off.
I will try that.
I'm also updating the firmware on the Zyxel router.