You can view your balance with your public key (=bitcoin address, looks like
1ExampleYk6vmtzVj4W71Xz1KzVM7Xccqe). You dont need to enter your private key (looks like
KExampleejLxb6e5Y3SfXZr1zYdi2xnNhEacygbceCCHgHa1hGyp) to see your balance, only when you need to spend bitcoin.
You can check balance of bitcoin addresses (one address per line) here:
http://www.homebitcoin.com/easybalance/Or enter your bitcoin address into any block explorer such as
https://chain.soIf you only know your private keys and not the corresponding bitcoin addresses, you can import them into a desktop wallet to see the bitcoin address and balance, or you can enter your private key into New transaction in
https://coinb.in to see the balance and the corresponding bitcoin address. Coinb.in runs clientside in your browser (JavaScript) and the private key is never transferred to their servers. You can also download the code and run it offline for more security but you cant retrieve unspent inputs or broadcast tx without internet.