Thanks jhyamma and guruji,

Then in this case, I need to apply OPT before return back to Nepal to maintain status? But OPT will expire after 3 months if not get job, right? So its not good to go Nepal and stay more than 6 months ?? So still confuse about my VISA. As jhyamma said " My VISA will not valid". Need to apply new VISA even though I have unexpired VISA...what you guys suggest ? Is it  safe to go Nepal and stay as much as I like and come to US with new I-20 before expiring my VISA? What will be the best idea! I wanna come back US but I don't wanna stay here with out job in this recession period. And always there might be some risk for Visa if my current unexperied VISA will not work. What to do? Big trouble and confusion still...........