i780 Sluggish and Unresponsive

I bought my i780 back in April and I am using it on AT&T in the US. I can live without 3G, so up until now everything has been fine, but all of a sudden my phone has become almost completely unusable.

I went on vacation last week to Mexico and noticed that unlocking it had started to take a long time. I would enter the PIN and the screen would take a while to paint. This got worse over the next few days and now I experience some or all of the following:

After unlocking, the response is now very slow - I press the screen or a key and it might be over 30 seconds before the action is performed.
The upper and lower bands (i.e. where the notification icons and softkeys live) sometimes don't appear on the screen or take a very long time.
The screen is functional, but the Start menu is missing and can't be activated by pressing the Start button.
Sometimes when the backlight turns off, pressing the power button to bring it back gives me just the lower band with an Unlock button that does nothing when I press it.

I had only a few extra apps on the phone (SPB Shell, Google Maps, Windows Live) and I have removed them all. When I can access it, the Memory control panel shows that I have about 2/3 of my memory unused. I have an active Exchange Server connection and I have about 1500 SMS in my Inbox as well.

Any ideas? Is it a hardware problem? Is there anything I can try before succumbing to a hard reset? Could something in WM have developed a "leak"? It really seems like an overtaxed CPU or something.

Thanks!

If it is something hammering the CPU you should notice significant battery life reduction. Has your battery been running down quicker than usual?

It could be something that is running when you phone starts. To check this go to \Windows\Startup using the File Manager and have a look what shortcuts are in there. If you aren't sure what is normal and what isn't you could move all the shortcuts to another folder on the device and restart the phone. If the problem has gone away it was one of those startup apps causing the problem. You can then move each shortcut back one at a time restarting after each one until you find the problem app.

Failing that I would backup what you can and do a full reset.