i have been getting problems with online shopping carts, when i add
more items the previous ones disappear and sometimes i can't porceed
to checkout at all because it gives me an error message that i have no
items in my cart.
i have Internet Explorer ver. 6 and cookies are enabled so are session cookies.

can someone please help me solve this problem.

Have you tried flushing your cache and clearing out all cookies BEFORE
you register with the site?  Many times, issues like this are caused
because some pages or cookies get corrupted.

Have you tried clear your Cache  and cookies?
I Think you'd better check your ie actives,because some shop website
need down actives,if not ,restat you computer, then go that
website.and check.

Hi desert_rose,

If everything is all right and set properly on your Internet Explorer 
the shopping carts items may also be disappearing.It depends on the
skills the website used.
 
I know the customer and cart items info can be stored in the website
server but not in customer cookies.In this case,cart items may
disappearing when a customer shops too long (time is set in
server,default 15 mins) and the server closes the session when timeout
just like you log out the shopping website so that your cart items
also disappears and your personal info is also disappearing.

Install FireFox and try, if the problem goes away, this might be the
problem with the browser. If the problem does not go away, it is the
problem with the site.