Help me get my homegroup back

So several months ago I noticed my laptop was starting to act funny when trying to access files over the homegroup on my desktop--it was asking me for my credentials every time I restarted the computer, and wouldn't remember them even when I checked the box. As best I could tell it was using my computer's name as my domain, so when I typed in the username/password I also had to type in the "domain" of my desktop, which was simply its name.

Anyway, I didn't think much of it until recently I wanted to fix this problem, and I noticed more problems. I first removed both computers from the homegroup. Then, I tried to make a new homegroup on my laptop. But attempting this results in the error message you see in the thread title, and no error code at all.

However, I can still create a homegroup with my desktop, and I can even join that homegroup from my laptop. But after joining, I cannot access the video/audo/photo folders that are shared on the desktop and the icons for them are generic, not the unique ones for each folder type. However, once I share any additional folders from the desktop, I can then access all the folders from the laptop, once I have entered the same login information it had started asking me for weeks ago. Oddly, my desktop can access those same folders on my laptop without any trouble, as could my wife's laptop!

I have scoured the Internets looking for answers. I've tried several solutions, but to no avail.

Just to be clear what I have tried so far:

1. deleting everything in the \Windows\ServiceProfiles\LocalService\AppData\Roaming\PeerNetworking folder and rebooting

2. checking the correct services were turned on.

3. ensured all computer names are different

4. tried two different routers, in case it was a hardware problem (one router is the one on which I had no problem using homegroups until a month ago)

5. checking IPv6 is enabled, and adding the registry edit mentioned elsewhere to ensure it is enabled.

6. the usual homegroup troubleshooting, on both the laptop and the desktop

7. deleted all my Windows credentials

8. synced the clocks/timezones

9. tried using a wired connection. The desktop is on wi-fi as well, though, and has no problems.

I think that's about it.

Tech details:
Windows 7 Home Premium x64
Alienware M11x R3 w/Killer Wireless-N 1103
Linksys WRT-160N with DD-WRT (original router)
TP-Link WDR-3300 with stock firmware (new router)

tl;dr: Homegroup feature stopped working correctly on my laptop. Tried lots of stuff, nothing has fixed it.

Not super urgent as Windows' regular networking function works, but it's bugging the heck out of me that I can't find a solution short of completely reinstalling Windows, which I'd rather not do. I figure if anyone knows a fix, it'll be you guys!