Sandy, if you've used the Add to Cart widget it only allows for a limited number of PayPal button images.
I would need to see the source code of a sample page with your image before I could work out what has changed.

Did you previously use the Customise button option where you include your own button image?
Its possible that if you've not Named this image or not included it in your website upload then PayPal has reverted to its default.

I think you've omitted this step.

Acorn

The purple bold bit should be your image...

<form action="https://www.paypal.com/cgi-bin/webscr" method="post" target="_top">
<input type="hidden" name="cmd" value="_donations">
<input type="hidden" name="business" value="1@2.com">
<input type="hidden" name="lc" value="US">
<input type="hidden" name="item_name" value="Fred">
<input type="hidden" name="no_note" value="0">
<input type="hidden" name="currency_code" value="USD">
<input type="hidden" name="bn" value="PP-DonationsBF:btn_donateCC_LG.gif:NonHostedGuest">
<input type="image" src="https://www.paypalobjects.com/en_US/...onateCC_LG.gif" border="0" name="submit" alt="PayPal - The safer, easier way to pay online!">
<img alt="" border="0" src="https://www.paypalobjects.com/en_US/i/scr/pixel.gif" width="1" height="1">
</form>