I know this is an old post, perhaps the following could help someone to connect using dhcp.
At one time dhcp worked on the Toshiba when one day "poof!" stopped working.
I did quite a few things on a Toshiba L755 laptop trying to restore automatic dhcp connections.
installed drivers, deleted drivers, reset tcp/ip using netsh, changed registry using microsoft fixits, changed registry manually, ipconfig/flushdns, removed anti-virus, checked for malware, rootkits and other unfriendlies, Unchecked ipv6 and misc ipv6 settings per techs suggestions. The only way I could connect was to manually type in network ip info for the wireless nic.
The list continues. But that is not why I'm posting.
I had almost given up and was resigned to the strange thought that even when all my other computers did not have any problems connecting to my wireless "n" router, the Toshiba L755 could not obtain a dhcp lease. Until I came across a website with instructions on clearing ipv6 "neighbors" and "destinationcache".
I was using ipv4 and doing the above makes no sense, At least to me. Well, I had nothing to use so I followed the instructions to clear and remove.
Opened up a cmd shell and typed the following:
first command was
netsh interface ipv6 show neighbors
netsh interface ipv6 delete neighbors
second command was:
netsh interface ipv6 show destinationcache
netsh interface ipv6 delete destinationcache
I removed the static ip I had set in the wireless nic and reconnected with a big sigh. Didn't expect anything since it was ipv6 and I'm using ipv4.
To my surprise, it connected for the first time since losing the ability to obtain a dhcp lease.
4 reboots later it was still working.
So, did doing the above fix it? I don't know. My dogs like typing on the computer and perhaps, just perhaps they entered in some registry settings which made it work, when I wasn't looking.
Or it's all just a coincidence. Either way, if you were just as frustrated as me, it can't hurt to try. If it doesn't work, well, on to the next possible solution.