Some customers cannot click in boxes

Hi,
I operate several e-commerce sites using Zen-cart. Recently, I have noticed a drop in sales and quite a few customers are phoning up saying that they are unable to click in the boxes on the account sign up form. One customer told me that if he/she clicks on the vey far left of the 'First Name' box that they are then able to enter their information wheras before they were unable to enter their details. I am unable to replicate this fault from my end and have no idea what is going on. I have re-installed the core template files but the problem persists. Can anybody give me a clue as to where to start looking or what may be causing this? The customers I have spoken to seem all to be using IE7 if that helps any.
:frusty:

Maybe you've got an XHTML validation problem in your site template, causing some browsers to not display the page properly?
Or some sort of javascript addon doing similarly?
Or maybe something in your CSS is positioning things wrong such that the fields aren't clickable due to something (invisible) being in the way?

Thanks for the advice DrByte. I have found a number of XHTML validation problems and am in the process of rectifying them - do not know whether or not it will fix my problem though ... but its a starting place. My CSS positioning things incorrectly seems both plausible and likely as the customers can access the boxes from just one corner, I will look into this definately. If this is the cause however, how come most people can access the form OK and others not? Wouldn't everyone have the same problem? Thanks again - I know your a busy person and appreciate your help.
:smile:

Wouldn't everyone have the same problem?

No, not all browsers interpret the box model the same way and it makes for lots of fun with CSS ...

Thanks guys - going to do a bit of fishing around!
:lamo: