●Clock (pixel frequency) adjusts the number of pixels scanned by one Horizontal sweep. If the frequency is not correct, the screen shows vertical Stripes and the picture does not have the correct width.
●Phase adjusts the phase of the pixel clock signal. With a wrong phase adjustment, the picture has horizontal disturbances in light picture.
4.When the image no longer looks distorted, save the Clock and Phase adjustments.
5.Press 
to leave the OSD menu.
Manually installing the monitor driver
Below are steps for manually installing the monitor driver in Microsoft Windows 7, Microsoft Windows Vista,Microsoft Windows XP.
Installing the monitor driver in Windows 7
To install the device driver in Microsoft® Windows 7, do the following:
Note: You must download files from the Lenovo Monitor CD to use the Plug and Play feature in Windows 7.
1.Turn off the computer and all attached devices.
2.Ensure that the monitor is connected correctly.
3.Turn on the monitor and then the system unit. Allow your computer to start the Windows 7 operating system.
4.Open the Display Properties window by clicking Start, Control Panel and then
5.Click the Personalization icon.
6.Click the Display Settings icon.
7.Click the Adjust Resolution button.
8.Click the Advanced Settings button.
9.Click the Monitor tab.
10.Click the Properties button.
11.Click the Driver tab.
12.Open the "Update Driver
13.Select “Let me pick from a list of device drivers on my computer” and then click the Next button.
14.Insert the Lenovo Monitor CD into the CD drive and click the Have Disk button.
Click on the Browse button and navigate to the following directory:
X:\Monitor Drivers\ (where X is the drive letter designator for the
15.Select the " L2251pwD.inf " file and click the Open button. Click the OK button.
16.Select L2251pwD and click Next. The files will be copied from the CD to your hard disk drive.
17.Close all open windows and remove the CD.
18.Restart the computer.
The system will automatically select the maximum refresh rate and corresponding Color Matching Profiles.
Note: On LCD monitors, unlike CRTs, a faster refresh rate does not improve display quality. Lenovo recommends using either 1680 x 1050 at a refresh rate of 60 Hz, or 640 x 480 at a refresh rate of 60 Hz.