As Crazy said, contact the bank to confirm if your check has been cashed at all. If so, and newegg says they didn't do it, have the bank reverse it and consider it as forgery/stolen. You may have to pay a penalty, but that depends on the bank you use.
The check number is on the top right corner of the check when you wrote it out. Are you using your own personal checking account, or your mom, and who signed for it? You should have recorded the check number, date, recipient, and amount in your check book (Congratulations! This is called account reconciliation, one of the skills we accountants have to learn fast).