Hi
Close Windows Defender from system tray, Right click the little icon next to the clock and select Exit.
If you delete the old update, checking for new updates will work.
To do this, Press Start > Run and type Msiexec /x {A5CC2A09-E9D3-49EC-923D-03874BBD4C2C} and click OK (you can copy and paste the Msiexec bit).
Open Windows Defender and check for updates.
If the above fails, try the following:
Windows XP and Windows Server 2003
1. Click Start, click Run, type wuaucpl.cpl, and then click OK.
2. Click Automatic (Recommended), and then click OK.
Windows Vista
1. Click the Start Orb, click All Programs, and then click Windows Update.
2. In the left pane, click Change settings.
3. Click to select Install updates automatically (recommended).
4. Under Recommended updates, select the Include recommended updates when downloading, installing, or notifying me about updates check box, and then click OK.
User Access Control - If you are prompted for an administrator password or for confirmation, type the password, or provide confirmation.
