General
My site looks fine on my computer, but when I publish to the internet things go wrong.
There could be any number of causes - in fact there is probably more than one problem. The key is to identify and tackle each problem one at a time.
My site works in some browsers (eg Internet Explorer) but not others.
This is especially common when using Microsoft products such as Frontpage. The bottom line is that your web pages need to conform to common HTML standards. You will need to go through your site and find which parts aren't standard HTML.
My site doesn't show up on the seach engines.
This is a whole field of study in itself. A good place to start is www.searchenginewatch.com.
I Can't Access my Website.
First of all, don't panic - most problems like this are temporary. To try and identify the cause click here.
Images
There is a blank space where an image is supposed to be.
Either the image file doesn't exist, or the image tag in your web page is looking for the file in the wrong place. Right-click the space where the image should be and select "Properties". See the "Internet Address" (the URL of the image file) - this is what the image tag is looking for. Make sure that the image actually exists at this location, or change the image tag to point to the correct location. See Introduction to Web Design: HTML
Images take a long time to load.
The file size is too big. See Graphics: Working With Internet Images.
HTML
A hyperlink doesn't work
Examine the hyperlink tag - you will have done something wrong. See the Hyperlink Quick Guide for more information.
My Web Page Doesn't Fit on the Screen (I have to scroll left and right)
See How to Fix Page Width Problems
Embedded Object Activation Message
Internet Explorer gives me a message saying "Press SPACEBAR or ENTER to activate and use this control". This is a common problem — see the Object Activation Workaround.