Checkout not working please help!

Hello, recently I have been getting a lot of emails and calls from customers of my online store saying that they can not complete the check out process. They are saying that the button to continue check out is not appearing for them. Their comments are pretty vague. I do see a few orders coming in, but i also see a lot of accounts created in the store with no orders and then I get all these calls.

I am able to complete the checkout process myself but can't work out what their problem is.

Can anyone help? Please I'm desperate as I need to take advantage of increased holiday sales but this little issue is costing me!

Webstore is at http://www.shainsware.com/site/

Thanks to all that may try and assist me...

Is this maybe a cookie issue or related to their browser security?

It worked for me, it let me go to checkout step 1, payment method step 2, there was a checkout button in the shopping cart page, but if you press continue shopping you would have to know how to get back to the shopping cart, now on most web sites it on the top like yours, but everybody does not seem to know that, I don't see anything wrong with your store maybe people are have trouble finding the shopping cart!

Thanks so much for taking the time to test that for me. greatly appreciated.

I have tested it in IE and FireFox with a whole slew of different security options and it always seems to work for me. Must be user error.