hmmm...........same story here!!!
i first subscribe to PTCL in 2007.......they provided me a ZTE Modem......used it for like 7 months.........WITHOUT ANY PROBLEM........i always recommended it to my friends!!!!
but then i switched to Wateen but the downloading limit made me go back to PTCL.........so this time they provided me a Shiro modem.............and my God, what a POS it was :@ always restarting due to voltage fluctuation........always getting hot.........literally had to shove it in the freezer to cool it down,,,,,,,,,,,,so after numerous calls they exchanged it with a ZTE Modem.........so things are going fine now but still they dont provide the same reliable connection that they did way back in 07...!!!
So my advice, get rid of the Shiro modem ASAP!!!