You have two computers with different problems. I'm going to suggest that you address these problems one at a time. Let's start with the first computer you posted about.
Please post the make and model of this computer.
What exactly happens when you try to boot this computer?
What error messages are you getting, please post the exact error.
About chkdsk, chkdsk is a command which has to be executed in the Elevated Command Prompt. Since you can not boot into Windows you can not open the Elevated Command Prompt from there. You will need the Windows 7 installation disk or have it loaded on a flash drive. You "command code", how and or where did you enter the command?
To run chkdsk /r (the /r switch has the functionality of the /f switch with the additional analysis of physical disk errors) Click on the Start orb , then type in cmd in the Search programs and files box. When cmd is seen in Programs above the Search box right click on it, then click on Run as administrator.
You will see a screen similar to the one below.
Copy and paste chkdsk /r in the command prompt, then press Enter. Please note: If this is a SSD, do not run the /r switch, use the /f switch.
You will receieve the message "CHKDSK cannot be run because it is in use by another process. Would you like to schedule this volume to be checked the next time the system restarts? <Y/N>".
Type in Y and press Enter.
Restart your computer to start the scan.