Based on my android keystore I created some apps. now, I want to update one of my programs but I lost my keystore. can I generate another one and update my app?
You can create a new keystore, but the Android Market wont allow you to upload the apk as an update - worse still, if you try uploading the apk as a new app it will not allow it either as it knows there is a 'different' version of the same apk already in the market even if you delete your previous version from the market
Do your absolute best to find that keystore!!
When you find it, email it to yourself so you have a copy on your gmail that you can go and get in the case you loose it from your hard drive!
No, there is no chance to do that. You just learned how important a backup can be.