VPN randomly will not connect. What could cause this?

My Dad works for a company that is centralized in Den. CO. They have employees set out throughout the country, one of which is my dad.

They use a VPN to allow these employees to access their email and files anywhere they are. It was workinng just fine [it being the VPN connection on my dad's computer], then one day it won't connect at all. We have to unplug all the internet related devices and boot them back up. After we unplug and plug back in, everything works great again.

This worked for about 3 months, then it happened again today.

Our internet route\path is as follow

Internet-->Cable Modem-->Vonage Phone Modem\Router-->Linksys Wireless Router-->then out to all 5 computers\gamesystems (2 wired CPU's , 2 wireless CPU's, and wired 1 Xbox 360.

Personally I think its the vonage phone modem. It's designed to be a phone modem for internet phone, not a full bow router. They aren't a router making company. But that's just my opinion. What is your guy's opinion?

I'm pretty good with computers, so please don't give me any junk asnwers. Otherwise I will report you. Thanks!

I agree with you the phone modem from vonage is not supposed to be a router.I have my vonage line as such. phone line to vonage modem. from dsl router to vonage modem 1 ethernet cable.
router=
1 phone line in
then all other ethernet connections out to my other computers.
if you have other stuff connected to the vonage modem take it off and put it on the DSL router. see if this helps.
if all else fails have your dad call co.headquaters and talk to the IT people and see if they can help.

You can try a few things. Narrow this down. Does the VPN fail at times only when you connect throught the vonage phone router? Can you work around it or bypass the modem? Has he tried connecting someplace else, like a library or McDonalds that offeres a wifi? WE usually reinstall the VPN software and that fixes many issues, but it also depends on what error is coming back, We have a cisco vpn program and the codes tell us what is exactly happening. If you think it is the modem, does it have a program you can access it? Check your gateway IP, and they type it into your IE address bar, you will need a username and password if this works. You can check if there are some settings that stop it from connecting.
You probably need a real router, unless tha vonage is actually detailed to run so many computer connections like what you have.