Error: Disk Utility can't repair this disk. Back up as many of your files as possible, reformat the disk, and restore your backed-up files

Hi.

My 1,5-year old macbook pro crashed (file system OS Extended (Journaled)) suddenly and only window I can see is OS X Utilities with 4 options. I read that I have to pick "Disk Utility". So I did. I chose "Macintosh HD" (it's grey) from left side and hit "Repair Disk" ("Verify Disk Permissions" and "Repair Disk Permissions" are grey). Result: "Error: Disk Utility can't repair this disk. Back up as many of your files as possible, reformat the disk, and restore your backed-up files." How can I back up my files? I've got a PC and an external hard drive WD My Passport.

Please help!