Cydia not opening after I reboot iphone! this is very common and it happens almost with all people who jailbreak their iphones. The Cydia problem can be observed in different conditions i.e. when you have jailbroken idevice with working Cydia previously or a new jailbreak is done. Mostly problem happens when people are having tethered jailbreak and their device is rebooted, in that case many people don’t know that they have tethered jailbreak. Also in the case of tethered jailbreak both Cydia and Safari don’t work.
Cydia not opening after reboot iphone – Tethered Jailbreak
So you must first of all check whether you have a tethered jailbreak or not. If you have jailbroken ios 5.1 then it will be a tethered jailbreak and each time you will need to boot tethered using redsn0w via your computer so that Cydia and Safari will open smoothly, and as a best option you can upgrade to 5.1.1 or 6.1.2 and jailbreak using Absinthe or evasi0n.
For jailborken devices also if you have ios 6.1.3 jailbroken which is only possible for iPhone 4, 3gs or ipod touch 4g then again if you reboot you need to boot tethered otherwise you will face same problem of Cydia not opening after reboot and Safari will also crash when you start it.
In above cases if you observe that even you have boot tethered and your device is still not running Cydia it means you need to re jailbreak and I recommend to upgrade to ios 6.1.2 for a smooth evsai0n jailbreak experience.
Cydia not opening after reboot iphone – Untethered
On the other hand if this problem of Cydia not working becomes on an untethered jailbroken device then a simple solution is to reboot your device for which I suggest to press and hold both power and home buttons until your idevice turns off and then turn on again just release both buttons once you see Apple icon on the screen, this reboot will solve the problem surely.