Normally, when a modem doesn't sync or syncs only periodically, (please differentiate a modem that is connected but blocked by Vidéotron and one that does not sync. Call the technical support if you think you might be) the problem comes from RF signals that are either too high or too low. Certain cable modems will allow you to access a web interface situated at the IP address 192.168.100.1 that will let you see current RF signals in db, which are incoming (RF), outgoing (TX) and noise (SN) signals. Here are the normal and acceptable ranges for these signals:

Signals:

• RX
  -15db to 15db
  
  
• TX
  20 to 57db
  
  
• RX
  Must be superior to 29db

Please take note that these values are considered as the highest acceptable values by any modems. If any of these numbers are over these maximums, even momentarily, it will inevitably create problems. The best test you can make is to connect your modem in the cable entry of your house. You will then be able to calculate the difference between the values you got at the entry and the first spot where you made the test and it will make it easier to find the source of the problem (bad house cabling, bad splitter, etc.). An easier solution is to call the technical support, but it can save a technician a trip if you make it on your own or save yourself some precious time of waiting for one :)

Also known as "Connect, can't browse", this problem usually arises when the user cannot naviguate and Vidéotron is not experiencing any server problems. Very often, the problem comes from active spywares on your computer that are corrupting registry files and TCP/IP protocols. They can can deleted by anti-spyware programs and keep your computer safe from any further intrusions. You can consult this guide on how they work.

There is a bug that currently exists on onboard motherboards where a MAC address will be duplicated. A MAC address works as your street address. Therefore, it is obvious there cannot be another MAC address identical to yours! (have you even seen anyone else with the same street address as you?) Certain motherboards all have the same MAC address and won't allow a stable connection. Although very rare, these problems can be solved with a patch from the board's manufacturer website.

Here are some known duplicated MAC addresses:

Nvidia motherboards: 00044B808003
Asus motherboards: 00E0006095566 & F6F000E73900
Ecs motherboards: 000795DDF26C & 0007954410DB
Realtek 8139 PCI motherboards: 0048543F7CCE