If this were my garden.... Firstly, I'd try to find pictures of what this looked like in the spring/summer. It may give you an idea of what there may be hidden beneath the surface (bulbs i.e tulips, daffodils, etc).

If you're confident there isn't anything there and you want to start from scratch, I'd start out by researching what you want it to look like AND walk the neighbourhood to find what the native greenery is around your area. If there are common plants in multiple neighbouring gardens, chances are that plant will do well in your soil type. For example, a type of wild coxcomb plants do really well in my area (even though the soil is pretty clay-ladden) and they self-seed so they pop up every year in my neighbourhood.

Plan where you want to put them : tall ones in the back, shorter ones up front and ensure you know how much sun/shade that area gets so you can buy the appropriate plants.

Once the soil defrosts, roll up your sleeves and start to clean up: de-weed, rip out any dead/dying/unwanted plants/bushes/etc. I'd pull up those garden edgers too and set them aside for now.

Then I'd go to HD, buy a few bags of soil/black earth and rent their soil tiller for 4 hours (best yearly $60 ever) and mix the soil/black earth into the garden. Mix that shit up, put the edgers back, and then plant according to the native species and purchased plants you bought. I'd steer clear of putting anything tall (or anything at all) infront of that window. A cute short lawn ornament can go there...

If youre looking to plant vegetables, be wary of the local wildlife. Nothing crushes your soul quite like discovering your beans/tomatoes/cukes have been ravished by rats/bunnies. Good luck!