Check for overlaps if a signal to the modem any items. It is possible that the communication quality deteriorates from what the modem is, for example, in the case of the computer near the wall. In this case, use the USB connectors on the front panel of the system unit, if any model of the computer case, or buy a special wire extension cable and install the modem in a location where the signal will be better.
If you use a laptop or a netbook, check that the signal do not overlap other objects or your hand. When using the wireless mouse, or Bluetooth connection on your computer at the same time with the modem, make sure that signals do not interfere with each other. If your computer model is possible, position these devices to the ports on different sides of the body. The same applies to the computer that simultaneously uses several active wireless devices.
If you are outside the house, and the level of the received USB modem signal got worse, change your location to the quality of communication became better (usually closer to the towers MTS). Also the signal quality is poor when using a USB modem in the basement and extremely isolated areas.
Check whether the slowdown is a fault of your modem. If your phone supports 3G, check the signal level of the MTS in your location. Also check whether the slow loading speed of web pages the result of a slow browser to do this, open any other browser and see the change of speed.
View the load on system resources in task Manager, maybe problems with the Internet caused by lack of RAM or CPU frequencies to perform the necessary operations.