These instruction are assuming that you are using Internet Explorer.
To accept "Cookies" you will have to lower you privacy setting, as it is too high and is rejecting the required cookie from PayPal. To always solve the problem click on "tools" in the upper right of the Internet Explorer browser screen, then on "Internet options". Then click on the tab "Privacy". It needs to be on low in order to enable the required Cookie, or you can make it site specific, which is very safe (security wise). Just click the button "Sites" on the "Privacy" page. It will bring up a window with a line to enter a site name. Enter "paypal.com" and click on the "allow" button.
You should have no more issues with paypal.
Hope this helps,
Craig