Okay so I have a computer here that refuses to log in to any website that requires a username and password...
Like techspot... can't login here on that computer... or DeviantART... or what ever...
I can't see why it would do this... it times out or something and says 400 bad request.
???

most logins require use of port 443. Make sure your firewall allows outbound port 443
(ie secured transactions).

Hmmm... that could be problem... is it possible that a linksys router's firewall is blocking it? Cause that's the only firewall (Other than windows firewall...) that's in effect...

not likely on the router. more likely on your system firewall OR even the browser
on IE ->Tools->Internet Options->Advanced
scroll for

Htt1 1.1 settings
Use SSL 2.0
Use SSL 3.0
Use TLS 1.1

and enable ALL of them

edit:
on FF->Tools->options->Advanced
enable both protocols
/edit

Okay, I'll try that.
On a strange note, disabling and enabling the wireless adapter, fixes this most of the time...
Which makes NO sense if it was a browser setting...
Maybe it has to do with the wireless driver having an error when the computer resumes from standby?

This computer also repetitively has a problem logging in to Google Talk... and it's fixed by the same enable/disable of the wireless adapter... so I'm going to make sure the latest version of the driver is installed along with any windows updates that this person (little brother) apparently has been skipping...

(On another note, the info here solved one of the problems on another computer in my house, so it was useful. Thanks everyone. ^_^)

"On a strange note, disabling and enabling the wireless adapter, fixes this most of the time..."

You can also try disconnecting the power from both the router and modem, waiting about 10-15 seconds and then reconnecting. This is called 'power cycling'. It clears the memory in the router and is necessary occasionally.

IF you had significant problems accessing yesterday, so did I. I don't know where the breakdown was, but I had it in the AM and PM.

This login problem tends to happen when the computer is used at a public access point, one using a small router (linksys) that tends to see about 100 - 300 different computers per day...
I assume that the router probably needs to be "power cycled" or what ever, and it needs to have it's routing table cleared for certain, because I'm sure it has about 500 outdated MAC IDs...

But I don't have control of that access point... apparently my little brother says that this only happens away from home... so I'm gonna say it's probably a router problem...

oh my! Public routers can easily be overloaded (as well as corrupted).

NEVER login to a bank account (or something where you NEED privacy) when using a hotspot!

I don't care if someone has my freaking DeviantArt login... they can do what with that? Post nasty comments? Oooo... I'm scared...
I'm aware of what not to log into...
(As far as techspot... if they get this password they'll probably go like "wtf... i don't care" and throw it out... so I don't think that's such a concern...)

oops; sorry to have interrupted you ... go in peace pyro

jobeard, not sure what you mean by that last comment... but what ever...
We didn't have the problem this time... so I'm gonna go with that it was the router not liking the computer...

But as far as a solution for when it happens:
Disable wireless adapter.
Enable wireless adapter.
Connect to network.

Works every time ^_^. (Not the best, ultimate solution, but hey it works...)