After installing motorola SBG900 few days later my switch is dead

I recently installed motorola SBG900. few days later my Nortel Baystack 450-24T switch is dead (port lights flashing non stop). Replaced the swich with a different brand and one week later it is dead. These are not cheap switches. want to know what is going on before adding another switch.

I have been using these swiches for about 2 years with a dsl modem without a glitch.

Any info will be highly appreciated.

Thanks
Timbuktu