Hi redsn0w users! We're a community of volunteers answering jailbreaking and Cydia questions.
Troubleshooting steps if Cydia is crashing:
If you've rebooted your device and Cydia crashes when you try to open it, you probably have a tethered jailbreak. To make your jailbreak work properly: plug in your device, open up redsn0w, click "Extras", and then click "Just boot".
Troubleshooting steps if redsn0w doesn't seem to be working:
If you're trying to jailbreak an iPhone 3GS and redsn0w still doesn't work, make sure you've clicked the right choice when redsn0w asks if your device has an "old" or "newer (fixed)" bootrom. (In other words, try the process again and choose the other option.)
If you're trying to jailbreak an iPhone 3GS and also make it unlockable using the iPad baseband, redsn0w may crash if you install both Cydia and the iPad baseband at the same time. If you're seeing this problem, you can work around it by going through the jailbreaking process once just installing Cydia, and then a second time just installing the iPad baseband.