You can make a disk from an online iso or use the iso to make a usb installer. Either would serve the purpose of supplying a source of system files that are not corrupt. Here is a link to legal Windows 7 iso files in many languages from which you an make an installation DVD. You can also use it as a startup repair disk.
What are you using in terms of internet protection from malware, adware and viruses?
Was there an event that happened before the problem began? I am referring to some kind of update of addition of hardware or software?