You could try running Windows Update on the machine , and applying and updates to internet explorer. Not that you need the updates,just that it may well install the latest version and resolve the problem. Otherwise if you are running Windows XP you could try a system restore, back to a time when the problem didn't happen.
Otherwise really need more info - version of Windows, exact error etc.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix desktop pcs.