Bitcoin will not open instead I see: error loading blkindex.dat I have downloaded it onto my windows pc 3 separate times and each time it goes to start the program it shows the bitcoin wallet "loading addresses", then it's "loading block index" then my computer makes a noise and I receive this: error loading blkindex.dat. I click OK and it disappears with no options on how to fix. 

I'm not very computer savvy. Please help.
Close the client, go to C:\Users\(Your Username)\AppData\Roaming\Bitcoin and delete everything in the folder except for wallet.dat - do not delete wallet.dat under any circumstances (and empty your Recycle Bin), then restart the client. Somehow your block index file became corrupted.