Clear your cookies, history and cache first off.
Secondly, download Avast! AntiVirus and do a full system scan.
Following this, do a full system scan with Ad-Aware SE, and if you don't have Spybot: Search & Destroy, download it and do a scan with that after the Ad-Aware scan.
Then if that doesn't solve your problems, try resetting your router and modem, by holding down the reset button and/or turning it off, waiting about 30 seconds, and then turn it back on.
If it STILL doesn't work, and you're using wireless, right-click the little monitor button in the system tray, and click Repair. It should repair the connection. If not, double click on the monitor icon, and disconnect from your current connection, wait about 30 seconds, and then reconnect.
After doing all this, download any or all of the following three top-notch, best browsers out there: Opera, Avant Browser, and Firefox.