It could be any number of reasons for this. Check your system for any infection of bugs....ie malware, spyware and adware. Then check for virus's with your Anti Virus software you have installed. Then clean out your registry for any errors or anomalies. You could reset you IE 8 to default setting and clean it out as well by deleting the temp files, cookies, saved passwords and web info in the tools/internet options/browsing history - delete.