There are multiple causes for the slow speed. The most common one is related to your traffic amount. The carrier who issued the USB modem and the SIM card also implemented limits for the traffic you download or upload. You might need to check with their service operators to find out how much MB you have left according to your contract. This should easily solve your issue. Additionally, try to disable the Firewall on your computer. It's possible that the Internet speed to be limited for your connection. Go to Start > Control panel > System and Security > Windows Firewall > (left menu) Turn on or off Windows Firewall. Turn it off, reboot the PC, re-plug the USB modem, connect and then browse the Internet again.