It would help greatly if you could provide just a bit more information regarding your issue.
What type of account did you request a check from?
If you are talking about a bank account, I would contact the bank, and tell them you have not received the check.
Make sure whatever entity who is sending your payment has your correct mailing address.
Since we are online here, are you talking about an affiliate program. If so, you need to make sure you have reached the payout minimum, and check the TOS of the program to see what the payment process is. Some programs hold your funds for 30-60 days to protect them from fraud.
Like I say, without more information, it is hard to answer your question more precisely.
Hope this helps.