I have the same issue.
my one completed its update the other day, and now, when I plug it into my PC, (which has previously worked) it doesnt recognise my phone as a mass storage thingy.
the biggest pleasure of my phone, was the ability to just snap photos, and REALLY quickly drag and drop copies onto my laptop/PC.
now, when I plug in (via the HTC cable that came with the phone) to my (Win 7 PC), it shows "HTC_PN071" under 'my computer', but when I pick on it, it does nothing, the options to 'expand' is greyed out, and "open in new window" just opens a blank window.
Ontop of all this, Ive gone and updated HTC sync manager, which is saying "no phone connected" even though my phone is connected, and unlocked (as I have done hundreds of times before, and worked fine)
Also, interestingly, I now get two notifications, which I would post a screen shot of, but I cant get off my damned phone.
one is
</> MTP mode enabled
and the other
</> HTC Sync Manager
any suggestions appreciated.