How do I fix my computer when it's opening everything with Microsoft Word?

This can be caused by more than one thing.

Default Program Settings

Someone could have accidentally tampered with the default program settings which determines what your programs use to open.

Right-click on the icon of the program you want to open. Select "Open With" and choose the correct program from either the list or via the browse button.

Malware or virus

Your computer could have been hijacked by malware or a virus.

Download a free virus scan (Avast, AVG, Windows Security Essentials, to name a few free ones), then scan your PC.

After that, download Malware Bytes (free) and scan your computer with that, because virus scans are generally useless at detecting malware, while malware scans are useless at detecting viruses.

Restart your computer after both scans.

If you cannot open the scans due to the issues, try opening them in Safe Mode.

Executable files bug

If the problem still exists, it could be a known bug with executable files in Windows.

The fix for this depends on what operating system you have (XP, Vista, Windows 7, etc). An article has been provided below this answer which will tell you how to resolve the executable files bug for your operating system version. (May need to log in to see it, sorry).

Corrupt file associations

If none of the above do the trick, it could be caused by corruption in your file associations. This can be caused by various things, from bad software to malware (even if you removed the malware, problems may still exist if corruption occurs).

To resolve this, you will have to do a system restore to a previous date.

To help prevent this in the future, download CCleaner (it's free) which scans your computer for bad or corrupt files and fixes them (or removes the ones you really don't need).

If all else fails, you can try the free Microsoft Fix It program, which is downloadable through the link below. It is an automatic program which detects and tries to repair issues.

If that still does not work, your best bet is to visit a technician, letting them know that you have tried the steps above.