I actually telephoned TM Net to report the problem to them - my package would enable me to have a free replacement modem - but I couldn't wait forever for their service technician to get back to me. So I had to buy a new modem. Fixed it up at home and found that though I could connect the desktop computer by cable to the Internet, there was just no response when I hooked up the old router to it.
No other choice, then, but to replace the router as well. Luckily, I did have an additional router at home. Went through the whole process of installing it and heaved a big sigh of relief when my desktop detected the signal. Heaved a second sigh of relief when my MacBook then detected the wireless signal. Everything's back to normal, but I've got to think seriously about getting a good surge protector to protect my equipment from now on.
I believe that I'm still eligible for a replacement modem from TM Net. Got to follow up with them...
The old (left) and the new (right)