what wallet you use ? check your email . downnload backup and save in flashdisk or save place who never can steal or copy your private key .
"if you have a lot BTC"
I see you are new here so I will be nice. The standard way to make a post is:
1) Read the question
2) Answer the question if you know the answer
What you did was:
1) Skip the question
2) Write some random stuff unrelated to the question
Watch this:
Hello, If i back up my wallet on bitcoin qt and I have other computer with bitcoin qt downloaded too. If I paste my wallet.dat file on my other computer and I do some transactions, will my balance also updates on the first computer too? Can I run the same wallet on multiple computer at the same time? Anyone know? thanks.
Balances are not kept in your wallet.dat. The wallet balance is actually caclulated from the blockchain. What is actually in your wallet.dat is just your private keys. So, to answer your question, if you have multiple wallets that have the same set of private keys (the same wallet.dat file) then the balances in all of those wallets will be the same and will be kept in sync as each wallet calculates the balance from the set of private keys held in the wallet.dat file.
If you have any more questions just let me know.