No "Add to Cart" button on certain browsers

This is driving me nuts.

I'm getting many reports of no "add to cart button" available on the product page.

If I test it myself the button is just there. I tested all browsers like IE, FF, Safari and Chrome.
It is also working on some friends computers. Also on iPad and other tablets.

This way I cannot replicate the problem.

I'm using ver 1.53. No new installed plugins, no new design or layout etc.

Please help, need to fix this asap
Thanks!

This is the website: http://www.dl-sounds.com

I'm getting many reports of no "add to cart button" available on the product page
I tested all browsers like IE, FF, Safari and Chrome.
Suggest you ask them what browser they are using and the version

Also would suggest finding out what product(s). There may be something specific about the product type or something associated with other things on the page associated with the product.

While you are waiting for people tell you which browser chokes on your page, fix the 79 validation errors, that doesn't help and may be the cause.
The page also cannot find this:
stylesheet_main.css

kobra:

Suggest you ask them what browser they are using and the version

Yes I did. Some using Chrome on PC others Safari on Macbook Pro. I'm waiting for the versions.

mc12345678:

Also would suggest finding out what product(s). There may be something specific about the product type or something associated with other things on the page associated with the product.

I only use download products. No special attributes or something. I do use Specials and featured products but the Add to cart button is missing one every product.

torvista:

While you are waiting for people tell you which browser chokes on your page, fix the 79 validation errors, that doesn't help and may be the cause.
The page also cannot find this:
stylesheet_main.css

Yes, I know will need to fix those errors. Hmm missing stylesheet_main.css. Will have a look. Thanks!

The add to cart buttons are there, but display below the fold. That's maybe the reason why they're reported (by visitors too lazy to scroll down) as not being there?