Install ESET NOD32 Antivirus and run a "in-depth" scan http://www.nod32.com.sg/html/44/42/

Some malware is designed to block access to system tools in Microsoft Windows such as the Control Panel, Task Manager, Registry Editor, and Command Prompt. This is done by modifying the security policy settings of the operating system. These changes can be reversed using the Registry Editor, but if it has been disabled, the following alternative methods can be used.
Using Group Policy

Click Start → Run. The Run window will be displayed. Type gpedit.msc and click OK (Windows Vista users: Click Start, type gpedit.msc and press ENTER). Re-enable the Windows system tools by following the instructions below.

To enable the Control Panel:

-Open User Configuration → Administrative Templates → Control Panel
-Set the value of the Prohibit Access to the Control Panel option to Not configured or Enabled.
-Click OK.

To enable the Task Manager:

-Open User Configuration → Administrative Templates → System → Ctrl+Alt+Del Options
-Set the value of the Remove Task Manager option to Not configured or Enabled.
-Click OK.

To enable the Registry Editor:

-Open User Configuration → Administrative Templates → System
-Set the value of the Prevent access to registry editing tools option to Not configured or Enabled.
-Click OK.

To enable the Command Prompt:

-Open User Configuration → Administrative Templates → System
-Set the value of the Prevent access to the command prompt option to Not configured or Enabled.
-Click OK.

Using the REG command

This option can be used only if the Command Prompt window (Start → Run, type cmd, click OK) is available. The parameters of the REG command can be displayed by typing REG /? and pressing ENTER.

The parameter ADD adds new registry entries or modifies existing ones. For example:

* Activation of Control Panel: modify the "NoControlPanel" key in the section HKEY_CURRENT_USER/Software/Microsoft/Windows/CurrentVersion/policies/Explorer

Command:
REG ADD HKEY_CURRENT_USER/Software/Microsoft/Windows/Current/Version/Policies/System /v NoControlPanel /t reg_dword /d 0

* Activation of Task Manager: modify the "DisableTaskMgr" key in the section HKEY_CURRENT_USER/Software/Microsoft/Windows/Current/Version/Policies/System

Command:
REG ADD HKEY_CURRENT_USER/Software/Microsoft/Windows/Current/Version/Policies/System /v DisableTaskMgr /t reg_dword /d 0

* Activation of Registry Editor: modify the "DisableRegistryTools" key in the section HKEY_CURRENT_USER/Software/Microsoft/Windows/Current/Version/Policies/System

Command:
REG ADD HKEY_CURRENT_USER/Software/Microsoft/Windows/Current/Version/Policies/System /v DisableRegistryTools /t reg_dword /d 0
References :

start>all programs>accessories>system tools>system restore

pick a first option the click the date when ur computer are running fine..

then it will restore ur system…
References :