Ok, I had this problem before but not like this one. I am using iPhone 3GS running on ios 4.0.1. My battery was almost dying out around 30% and I was taking a video. Suddenly the camera app crashed and it restarted. Then I opened up photos and it started rebuilding library and stopped right towards the end. So I reset the settings through settings.app. After that, now none of the apps open. Neither settings.app nor mobilemediaplayer.app , nothing. The safe mode starts but I am stuck an hopeless. I am confused as to what's wrong. I'll give the crash log report soon.

My guess is that the phone died while recording and recorded a portion of video that is crashing the library when it is parsed. Is it possible for you to delete the video that was recording when the phone died in any way? I understand that a lot of apps don't open, but you could use an AFC enabled app like DiskAid, iPhoneBrowser, or iFunBox to access the Media directory and manually delete the offending file.

Thanks for the reply. Yes I did what you mentioned because I have dealt with this problem before. Now my camera and library works fine. But other than Cydia, Phone.app and Camera and Photos none of the apps (cydia apps/app store apps) open in the normal mode. They only open in safe mode. And its a pain using safe mode all the time. Any idea about such an error ? Is it because I did "reset settings" from the settings menu or some old Mobilesubstrate addon / cydia app which is causing this ?

Oh and if I restore my phone though iTunes will I lose my jailbreak ?

Unfortunately, unsure as to why Cydia/etc. would be crashing -- make sure you used a proper untethered jailbreak. Upgrading/Restoring through iTunes to a non-custom firmware will threaten both your jailbreak and any unlock on the device -- it is recommended that you only restore using custom IPSW and block baseband updates if you're relying on an unlock for your service.

Thanks a lot for clearing that up dude. I was just about to restore.. So which one should i use to jailbreak & unlock again. redsn0w or what ??.(serial number 86928........)
I am confused this time since i havent jailbroken my device ever since i had it done almost a year ago.