Problem with migrating to New Firefox Sync

I have Old Firefox Sync set up on a Dell laptop and an HP desktop. Both have Windows 7 64bit and (currently) Firefox 28. (Please ignore any data about the machine I am using for this question as it is irrelevant and does not have Firefox installed). Last year my old Dell WindowsXP laptop died whilst in use and the drive cannot be accessed. Now when I use Old Sync on my new Windows laptop or my desktop, "Tabs from other devices" lists the tabs that were open in my deceased laptop at the moment of death. In addition, I cannot, of course, remove Old Sync on that dead machine, and, according to the way I read your articles, I cannot set up New Sync without unlinking all machines. What should I do? Incidentally I have previously sought advice here as to how to remove the tabs that still appear to be coming from the dead laptop, but cannot get a sensible answer! I should be grateful for an intelligent and knowledgeable reply. Thank you