I do a volunteer thing every other Friday ansering phones for a hotline.  Between calls I can do what I want and I sometimes web surf.   Fora long time I was unable to use my HP laptop.   then i discovered that the reason was that the wifi chipset in the HP was incompatible with routers of a certain make and firmware.  When they updated the firmware my problem went away.  See if there is a firmware update for your modem.  You have nothing to lose.