the causes can be external and internal. try the followings:
(1) if you are using wireless, check if it's unsecured. if yes, change it to WEP or more restrictive one (to prevent others from using your bandwidth).
(2) power off your router and modem. unplug power cords for both, wait for 10 seconds then plug back in (this is to reset memory in those devices).
(3) clear your browser cache. if you are using ie, go to tools --> internet options --> click delete (also check "delete browing history on exit". if you are using chrome, options --> under the hood, click on clear history data.
(4) optimize your pc performance. there are many things to do on this, but couple easy things you can do -
a) clean disk;
b) defregment disk;
c) download super antispyware and do a complete scan;
d) install additional memory
e) uninstall unnecessary programs
d) * UNINSTALL all softwares originated from china (like qq, etc)
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