re: HP Envy Laptop, can't recover, can't format, can't f*cking deal with this.

I don't know anything about 8 vs 7, and honestly I haven't personally seen an MTU problem in years, but that set of symptoms -- ping works, DNS works, browse doesn't -- set off some dim and dusty memories. That's also something in the TCP stack (and local infrastructure) that could plausibly be different between wired and wireless.