The A key on my laptop won't go down - feels like something is blocking it- Can I fix this myself?

A crumb or piece of paper is a likely culpret. They are relatively fragile and there are key repair kits available, but I can't tell you how to take a key apart.

Take a stiff toothpick and lightly go around the edge of the key to see if you can find something and dig it out.

Another culpret for a sticking key is a spilled sugary drink. For that, keyboard removal and soaking in water and drying either outside on a warm day or in a bag of rice works. Set the KB on top of the rice and seal the Ziploc bag.

The keyboard is generally easy to replace.