Try opening Start and typing services.msc in the search box. A box comes up with all the services on your system.
Look down the list and see if Windows Search is enabled. Highlight it and look at the top left section of the box. It says Windows Search. If it's not running there should be a link there that says "start." Click to start the service.
If the status is Disabled, right click on the Windows Search line and select Properties. In Startup Type change it in the drop down box to Automatic (delayed start). Click OK. Now the link should be visible in the top left to start the service.
If the indexer is running and it still doesn't work, open Explorer to Computer, right click on the drive where search does not work. Click Properties. There should be a check box at the bottom to enable indexing the drive.
If none of this does it post back with what you find at each step.