Nightly crashes on Nexus S
My Sprint Nexus S 4G has been crashing frequently for the past 2+ weeks. The phone crashes consistently if left on overnight - alarms don't work and when I wake up the screen is usually blank (but still on) and the capacitive buttons below the screen are glowing. Nothing is responsive and I have to remove the battery to reboot, at which point a second crash often occurs, including the "dead android with red triangle" sign being displayed on the screen. (Occasionally the overnight crash will show a dim version of my home screen, instead of being completely blank.) Also, the phone sometimes goes abruptly to the dead android screen during the day.
I performed a factory data reset via the Settings menu, but that didn't help with the problem. I also recently had Sprint factory-flash the phone, also to no avail. I didn't install any new apps or take any other action around the time that the crashes began, so I don't know what could have happened. The only thing I've noticed is that crashes tend to take place after longer periods of inactivity (like being left on overnight).
Does anyone know what is going on? Any ideas on how to fix this? I don't carry insurance on my phone, and I can't currently afford to be without a phone for the 3 weeks Samsung says it may take to get it back. (I could always go to Samsung later, but I thought I should ask the geniuses here first.)
Many thanks for any advice! My relevant phone details are below.
Nexus S 4G
Thu Feb 2 16:56:02 PST 2012