since you are using a windows machine (vista,xp .7,8,or windows 10 )there can be many issues but most will get cover by this -
remove all unwanted toolbar , unwanted programs and unwanted softwares
upgrade the ram and clear the junks and check for any updates pending or antivirus issues for more visit hp [http://goo.gl/V9mzjm|http://support.hp.com/us-en/document/c03340676] hope that helps