hello, i have a problem, can anyone pls help me?

i had iota since the end of july, i have made the update with no problems, that was more than a mounth ago and today i entered my iota wallet and i  have 0 balance. I had version 2.4 and today, after i saw zero balance i have installed version 2.5.1.1 and i have 0 balance and no transaction history. what is happening?