Why Does Windows 7 32 Bit Restart Automatically After I Try To Shut It Down

OS: Win 7 32 bit

Ubuntu 11.14

When I press shutdown button in the OS platform (both in Win 7 and in Ubuntu), the laptop starts automatically. Similar things happen when I try it in Safe Mode (without Networking/ command prompt). When I pressed shutdown, everything goes normal, screen is shut down, Hard disk LED is turned off, but power LED stays on. And within 2-3 sec, Hard disk LED turns on automatically and laptop restarts automatically.

I have licensed and updated Kaspersky Internet security and also checked with Kaspersky online virus removal tool. No virus detected.

I have also tried changing “PowerdownAfterShutdown” value in registry: didnt work. Also tried with “Wake on LAN " solution: didnt work

Tried using RefreshPC as suggested in this forum: didnt work.

Please suggest some other solution. Could it be a hardware issue.