3GS jailbroken but network unavailaible

Hi all,
I have upgraded my iphone 3GS to iOS 6.1.3. after the upgrade, I did jailbreak it and did all which is said in the tutorials. I did install the ipad basbans and after downgraded it. after installing Ultrasnow ans ultrasnow fixer. now, I have no Service. sometimes, from 10 AM to 5 PM I get the network and Im able to call and send sms, after this time, the network disappears. please help me;; how can I fix it?