Thanks for answering this. Since posting this I've tried switching batteries on the motherboard, and directly connecting to my cable modem (removing the wireless router) but it hasn't made any difference. I did try a scan in safemode with Malwarebytes too.
I'll try your other suggestions. One of the posts I read said it could be a hardware problem - non-specific as to what. Again, I can't see how that would matter since Windows 10 is supposed to be pinging the Internet for the time settings. Also, someone said it could be a startup problem with another program taking control. I don't have any unusual programs running that I can see doing that. Mostly, ordinary stuff like Adobe, Office, etc.
One thing I have noticed is that when the PC boots up (very fast) it initially is not connected to the Internet and it takes a good 20 to 30 seconds to connect. Could it be that the time tries to ping the Internet when it's not connected and then doesn't try again after it is? Could this be a Ethernet driver issue? I checked and the Ethernet connection says the driver is OK - I even tried the automatic driver update but that lag is still there.
I'm not sure which specs you need. Here are some of them from CPU-Z:
Intel Processor 3.10 GHz
Core Speed 800.01MHz
Bus Speed 100. MHz
L1 & L2 Cache - 32 KBytes x4 8-way
L3 Cache 8MBytes 16-way
Mainboard Gigabyte Z97-HD3CP
Memory 8054 MBytes
Graphics and Audio are onboard.
Thanks for your help.