Wired internet and network access becomes very slow.
Wireless internet access remained at normal speed.
Multiple PCs/Mac experience same issues.

When I say slow, I mean ten times slower than dial-up!

The short answer: Replace the modem/router box.

The Ethernet ports in my router had failed. I replaced the router and was back to snappy internet and network performance in ten minutes. If your symptoms match mine, this could well be your problem. Because it might not be I would suggest that you read some more about what happened to me. Oh go on!

Because I run a vista machine at the moment I naturally made mistake number one. I googled for ‘vista very slow internet’. Don’t do that, whatever you do. If you do, and I did, then you will learn all about something called autotuning. Along the way you will learn to do things like run elevated command prompts, use the netsh command. You will read endless pages about TCP/IP protocols and then you will work out that there is in fact nothing wrong with your Vista after all.

Word of the day: truculent
–adjective
1. fierce; cruel; savagely brutal.
2. brutally harsh; vitriolic; scathing: his truculent criticism of her work.
3. aggressively hostile; belligerent.