Problem: Someone has sent me a document as an email attachment, but I can't open it, or when I do, it's all gobbledygook.

The reasons and the cure:

1. (Read) Someone's sent you a file which was created using a program which you don't have on your computer
2. (Read) For some reason, your computer has 'misread' the type of file that the attachment is - i.e. someone sends you a Word file, but your computer seems to think it's a graphics file
3. (Read) Someone sent you a file without a file extension in the filename
4. (Read)You did something terrible in a previous life, and this is your punishment.
5. (Read) You may well ask...

Microsoft Word® only: you have an earlier version of Word than the document you've received was created in. Read the simple but annoying solution

How do I know what's happened? What can I do about it? Read on...:

1. A program you don't have on your computer
Unrecognised file types (i.e. files created with a program which you don't have) are represented by this icon:. When you try and open a file like this, there's a whirr and a click, and then this dialog box:

What you see when you try and open a file which was created using a program which you don't have on your computer.

What to do:

a) Don't always believe your computer. Sometimes Windows gets forgetful. A file extension it has known about for years (i.e. *.doc) will suddenly show up as . All you need to do is scroll down the list of programs in the list above until you find Microsoft Word, select it, and press OK. If you think Windows is just being stupid (e.g. it ought to know that *.doc files open with Word) select "Always use this program to open these files".

b) Give up, go to your computer shop/internet and buy/download the program you need. The clue to what program has been used to create the file is in the file extension. Scroll down the file extensions page to see a table of common file extensions and the programs which are used to create them.

c) Email the person who sent the file, and ask them if they can send the file in an alternative format.
(Applies particularly to Microsoft Word® documents) People can be thoughtless, and send files that were created on some nifty little program that only they and ten other people own. Programs often have the option to 'export' files in different formats which the rest of the world can read. A classic example of this is Rich Text Format (*.rtf ) - if you have Word 6, but your friend has Word 2000, your friend should export their document as Richt Text Format, which Word 6 is able to read.

2. Computer misreads file extension

Example: someone sends you a Word document (dissertation.doc). Somehow (don't ask me how), your computer or email program has read this as dissertation.html, so instead of the Word icon (the big W) you get the Internet Explorer icon (the big E), since *.html is computer-speak for "please open this file with Internet Explorer".

How do you know? You don't, but if someone sends you a normal file which you reckon you should be able to open but you can't, you can try tricking your computer into reading the file properly, by changing the file extension into what you think it should be. Once you realise how crusty Windows can be at times, you'll see that this isn't high-tech nerdy stuff, it's day-to-day problem-solving.

What to do.
1. Select the file attachment and prepare to rename it. Step one can be done in three ways:

1. Right-click on the icon representing the file, and select "rename" or
2. Right-click on the icon representing the file, and select "Save As", and retype the name when prompted or
3. Select the icon and press F2 or

2. Retype the name, but put a different file extension, e.g

2. a) The file selected: (the green icon is the symbol for a Macromedia Dreamweaver ™ file)

2. b)The file after pressing F2/rename: note how a box has appeared around the file name, and a cursor appears, waiting for your input

2. c) The file now I have changed the extension to *.doc. Note that the icon has automatically changed to a Word icon.

When you double-click on this icon, you may well find that what appeared to be a corrupt or unrecognised file actually opens quite normally.

3. Filename with no file extension

This can happen

• when people send files from a Mac to a Windows computer
• when someone has renamed a file, but in the process, deleted the file extension

In both cases, you need to add the file extension to the filename yourself, having guessed what sort of file it was that your friend sent you. Trial and error doesn't hurt - you can always rename it back again. Follow the instructions in (2) above.

4. You did something terrible in a past life

This is frequently the most logical explanation for (2) above.

5. You may well ask:

If it's that simple, why doesn't that dialog box say "sorry, either Windows has screwed up, or you need to go and buy program x, because this computer doesn't have the right software to open this file? Have you thought of renaming the file?

I don't know. Thousands of people all around the world have to write pages like this one, to make up for deficient information, unhelpful menus and poor progam design from Microsoft.

How can a computer recognise a file extension one day, and not recognise it another?
I don't know. My own computer has days when it decides to change all the icons on the desktop into the wrong images. I've given up asking.