PSE 9 and PSE 10 can co-exist on the same PC - the reason I asked was to eliminate any hardware or Operating system differences.
If you start with PSE closed and your camera disconnected, what happens when you first connect your camera? - Does the downloader pop up or do you have to load PSE and do a get from camera?
What cameras are you connecting?
I'm assuming that you haven't changed the communication settings on the camera since you had it working on PSE 9.
No messages showing up on the camera?
I have been testing using a Canon SX30 and the autostart feature doesn't work there either - I think it is a funny with using 64bit system - is yours 32 or 64bit?
If you connect your camera and switch it on, does it show up in the Start -> Devices and Printers list?
If there, double click on the camera and that should open another window
You should be able to browse the camera and see the images on the card.
Are your options set correctly at Edit -> Preferences -> Camera or Card Reader?
There is a new version of the downloader out for a fix to the date problems. It shouldn't affect your situation but it might be worth a try.
The only other thing I can suggest at this stage is to uninstall PSE 10 and install it again. It seems as though one of the files has become corrupt.