How to retrieve lost private key

[Best80]

Is there anyway or solution to retrieve a lost private key to myetherwallet?

[so_stupid]

then the feeling when too lazy to look in the search engine for such questions. 
No, it is impossible to restore, change, and other actions. Forget the old wallet. Start a new one 

[th3nolo]

Is there anyway or solution to retrieve a lost private key to myetherwallet?

Only if you have an archive of your wallet if not, then you have lost your wallet forever.

[Cult]

If you also generated a JSON(UTC) file, it may help as MEW enables logging in using the file and your password. If didn't, unfotunately recovering unsaved private key is impossible.