Few possibilities...
1)IE's screwed - check
www.windowsupdate.com for updates. If already up to date, from control panel Add/Remove Programs find Microsoft Internet Explorer, click the Remove button and select Repair from the dialog.
2)Your PC's date setting is wrong, double click the clock in the corner to check. Long shot, but it would explain this type of warning.
3)Just turn off the warnings. Tools/Internet Options/Advanced. Near the bottom uncheck Warn about invalid site certificates.
BTW, hold down ALT with PrintScrn to just capture the active window.