Keeping your computer system up-to-date is important, but every once in a while an update can cause a problem. Recently, Internet Explorer 9 caused some trouble with Intuit Merchant Services. In our office, what we saw is that hitting the "submit" button to complete a transaction did nothing at all (no error message, no response). If you clicked away to "cancel", then an error message would appear. Turns out there are several symptoms reported: web pages missing information or not rendering properly, downloads not working, "Page Cannot be Displayed" when accessing known good links, and similar problems.
For work arounds, go to the Intuit QuickBooks support page: http://support.quickbooks.intuit.com/support/Articles/SLN50403 Alternatively, transactions can be processed outside of QuickBooks through the Merchant Center - https://merchantcenter.intuit.com. You may not see any problems, and most of the early problems have been resolved, but if you see problem that can't be worked around, you can reach Intuit support at 800-558-9558.