The first thing to check is that the address(es) generated after you imported your private key(s) into Electrum are the same as the address(es) that you had in MultiBit Classic. If the address(es) are different, then you have imported the private keys for a different wallet.
Also, have you actually checked the address(es) from MBC on a block explorer like blockchain.info to see if they still contain BTC? It could be that the coins have already been spent and those addresses no longer contain coins, so that is why you get 0 balance. Does Electrum show transaction history?
Additionally, when you exported the keys from MBC, you need to make sure that you do not password protect the exported file and then you should have got a text file that listed all your keys in a format like this:
# KEEP YOUR PRIVATE KEYS SAFE !
# Anyone who can read this file can spend your bitcoin.
#
# Format:
# <Base58 encoded private key>[<whitespace>[<key createdAt>]]
#
# The Base58 encoded private keys are the same format as
# produced by the Satoshi client/ sipa dumpprivkey utility.
#
# Key createdAt is in UTC format as specified by ISO 8601
# e.g: 2011-12-31T16:42:00Z . The century, 'T' and 'Z' are mandatory
#
KyRmVbFNN95UUKBzVVkzC3xqoR4k6rrTBCsBpTTcxZBZCQzzhjfT 2009-10-27T22:04:57Z
# End of private keys
You only want to copy and paste the actual key (highlighted in red above) into Electrum... do not copy the datetime stamp at the end of each key, or any of the lines that start with a '#'