I haven't done anything unusual to my Volvo. Today, I tried to open the hood, but it wouldn't open. When I pull the white hood release handle, I don't hear the thump. I pushed and pulled the hood release, all to no avail. I manipulated the hood front and back, side to side, all to no avail. I was able to get the hood up about 1/4" and stuck a screwdriver in, but that didn't work either.

As Jp213a suggests. Reach up between grill and rad an move latching mech.

Your cable holdowns may be loose allowing cable sheath to move (rather than just the wire) when pulled.
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1980 245 Canadian B21A with SU carb and M46 trans

Lay under the radiator and look up in front of it to the bottom of the hood latch. You'll see where the release cable attaches. Try reaching up and working it by hand. Once the hood is open, check the cable hold downs, especially where it does a 90 around the battery. Mine was up against the battery and when I pulled the hood release, the battery would rock back. Now the cable is held to the sheetmetal cross member in front of the battery with a heavy plastic wire tie and it works fine. There was already a small hole in the cross member but I drilled it out a couple of sizes so a heavier wire tie would fit through. It doesn't hurt to grease the hood latch once in a while. jp

Two ways.
1.) Crawl under car ( car on jack stands), remove splash pan, reach up
and move latch release in direction of pull wire.

2.) Form a hook at the end of a heavy wire (old wire coat hanger type).
slip hook through grille, slip hook onto latch release, pull. May take
several tries. This is the only way a friend of mine can open his
hood (wire on in car release broke).

Your wire may be broke also, or the release mechanisim needs a good dose of grease.

Al