IN OTHER WORDS i CANT USE MY OLD ELECTRUM WALLET ,I HAVE TO SEND ALL MY BITCOINS ON LEDGER NANO WALLET AND AFTER THAT TO CREATE NEW ELECTRUM WALLET USING LEDGER NANO SEED?SHOULD I CREATE NEW ELECTRUM WALLET ON ANOTHER COMP. NOT ON THE ONE I HAD BEFORE?
You can have multiple Electrum wallets on the same PC so there is no issue with that. You can even have multiple wallets open at the same time.
You just need to create a new Electrum wallet with the Ledger Nano and select hardware wallet option during the creation as shown below:
Once that wallet is created, you can send the BTC from your other wallets to the new wallets.