i need help regarding walet ..

my coin is not showing after sync

but wallet adress showing the balance in blokchain explorer
Try to dump the privkey with the 'dumpprivkey "pubkey"' command. If you own the privkey, you own the asset.
currently iam trying . to resync wallet again but its take so long time

Dumping the privkey has nothing to do with syncing. Best you cut the network the wallet calms down, then you use the command to try to export the privkey.
then how to use that pvt key actually iam new to qt wallet
If you own the private key, you own the asset, independent of any working wallet. Thats's most important.
Have you been possible to export the private key?
yes exported the key.. but how to get my balance after that
Your balance can be seen with the coin explorer,
https://chainz.cryptoid.info/bean/ (Use the public key for this, of course)
I hope you see the balance as expected. Because you own the private key, you own the asset on this address. Perhaps you print the private key on your printer, that you have a backup of it, if the amount is significant for you.
Thereafter you can go on with creating a working wallet.