First thing you have to do is build the array from within the RAID bios.
Simply enabling the RAID controller does not do anything. You have to actually build the array and set it as active. There are several steps to doing this.
After you set the controller to RAID (and specifically the type of RAID you want), there is another setting in your BIOS....."Use RAID as storage", or "RAID as bootable". You have to set that.
Then, you have to set the RAID array in your boot order, if it is to be a bootable array.
THEN....when you boot, about 2/3 of the way through your POST screen you will notice a line that says something like "Press ctrl-8" or "Press F6" or something like that to enter the RAID BIOS.
Then you enter the RAID BIOS, and build the array you want from there.
Building the array can be complicated if you have never done it, so get your manual out and read it carefully.
After you have the array built in the RAID BIOS, THEN you reboot and start loading Windows. You will know if it set correctly because just after you see the line to enter the RAID bios during post, now you will see another screen of information that lists the drives in your array, and it will say something like:
SIL RAID SET...blah blah blah.......
WD 500 GB blah blah blah
WD 500 GB blah blah blah
RAID MIRROR SET AS DRIVE 0 ON CONTROLLER blah blah blah.....
Every controller displays this info a little differently, but you get the idea, you will see the info displayed that lets you know the array is intact and functional as far as the BIOS goes.
Be sure you install the correct RAID driver. There will be several of them, and if you do not choose the correct driver for the array you have built, Windows will not find the array.
If you are not experienced at this, save all your important data to an external drive. I guarentee you that you will be sorry if you don't.
Last but not least, if you are setting up RAID 1 as a sort of "backup", it is a bad idea. RAID 1 is for redundacy in case of a drive failure, the system can stay up until another drive is installed. It does NOT protect you from data loss, as a lot of people would believe.