My son used metal/steel 2by4x8ft's(studs) in his basement. I've heard some people use that type of thing in places with severe storms to keep house from ripping apart. But if you got to see it I don't know what kind of wood would be so dense. DH worked with wood & I think the 2 hardest were ebony & rosewood but they are much to expensive to ever be covered!! Burl is dense also but never would be used like that. Might get concrete bits for your drill. They would be able to get through it!!

1. Do you have sharp drill bits or are you using something that has been knocking around in a box since who knows when?

2. Do you have a reversible power drill with a lever that that may have accidentally been set to reverse? [The drill bit should be rotating clockwise as you look at it from the back end of the drill.]

If you are getting part way into the beam, it could be a flitch beam.

These are made by sandwiching a piece of steel between two pieces of wood.
The steel used is often very hard.

At least get a brand new drill bit and make sure it is turning the correct direction.

Where exactly in relation to window are you drilling? How are in are you getting before your drill stops? The link below will show the typical construction of a wall.

As Brickeyee mentioned you could have steel in the header above the window but in that case you should be bottoming out about 2" in (1/2 drywall plus 1 1/2" of wood).

Here is a link that might be useful:

Thanks guys. DH went and got new drill bits and different screws. I impatiently made a hole in the wall to see what was back there and right past the dryboard is a dense wood beam. For sure I wasn't drilling on the reverse setting but, I can see where you might check that first. This has happened in a few rooms and we got frustrated b/c didn't know what was back tehre. Even though DH is ticked i put a hole in the drywall to see, now we know what we are dealing with at least.

Thanks all. I'll let you know how it turns out.

Call Ripley's!

It doesn't add up: The exterior is brick, and the interior is plaster, and you are sure that the drill-rejecting material must be wood? It seems possible that your brick house has load-bearing high-fired tile block walls. Now that material is extremely difficult to drill into even with a hammer drill, if you happen to hit one of the webs.
Casey

There's something amiss here. Old wood can be a little dense and difficult to drive screw into but it shouldn't be a problem with a sharp drill bit. Certainly not a bit of the size one would use for pilots holes for screws to hang curtains.

You've seen wood?

How about adding a vertical trim boards under the ends of your curtain rods? That way the upper and lower ends of the vertical trim boards can be nailed into the wall areas that accept fasteners and then the curtain rods can be fastened to the vertical trim boards at the height you want your curtains.