It's unclear from your post whether you can still boot into Windows and manipulate files.
(Clicking Cancel means debugging Explorer, using whatever debugger you have installed.)
The possibilities are:
- A bad plugin installed in Explorer
- Virus infection that failed to take over Explorer
- Windows files are damaged
The possible solutions are in order: (1) find and uninstall plugin, (2) antivirus scans, (3) system repair, (4) total reinstall.
First, boot in Safe mode and see if this problem still arrives. If it doesn't happen any more, locate and uninstall the Explorer plugin. If none, locate and uninstall the product that causes the problem.
Use some antiviruses to deeply scan the hard disk. If you can't boot even in Safe mode, use a rescue live-CD virus scanner : I like best Avira AntiVir Rescue System because it gets updated several times a day and so the download CD is up-to-date.
If no virus is found, use sfc /scannow to repair important Windows files.
If that also doesn't work, you should Perform a Repair Installation.
If nothing works, you should format the hard disk and reinstall Windows. Save first all data, of course.