Internet connection quitting, think it's the modem

[Nightshade]

So, I've had the same setup for two years now, meaning the cable modem's been on the same line in the same room, etc. Recently I've started having problems wherein the connection just quits. I'll look at the modem and sure enough, it's lost the cable signal. This happens from my PC, laptop (wireless), and when I'm trying to play CoD3 online on my 360. My question is this: Are there any tools with which I can monitor the signal to the modem itself from my PC? I know I should put a meter on the coax and check the signal strength, but I don't have one. I know I should just call Time Warner and have them come out, but it's a pain in the ass, and I don't have the time off available. This would lead to the wife having to deal with the contractor morons that TW will send out, and I'd rather do that myself.
The modem's 5 years old, anyone else had a Toshiba PCX1100 go tits up on them?

[Foo]

Dig a little deeper into the router's logging and see if you can establish whether it's the router crashing, dropping the connection, or whether it points to the line itself.

With cable you're on a direct contention with your neighbours, literally on the same piece of wire in some cases I believe... so if someone's being a jackass down the road with something I can see that it might cause you problems.

[SplEEb]

If you rent your modem, call them without hesitation to
try a new one. Plus another thing that happened was
the overhead wire was all narled up at the loop and connection
at the pole. New wire and modem fixed all my issues.

[Nightshade]

I do rent the modem and I did get a new one. The tech support ox was surprised that my old one was still working. No problems seen so far, but I haven't tried CoD3 on Live yet...

[Scourge]

Yeah I had that same model go out on me after only a couple years. Got it replaced with a different model for free by the isp.