From the sound of things, you are better off bringing the laptop to a computer tech to check on.
You don't really explain the issue very well, by logon page do you mean the username and password screen of Windows? What OS are you running? Did something happen before this slowdown, virus messages, funny noises, etc..
What parition are you talking about, did you have the hard drive in 2 partitions and the other one is missing? Since you seem to be able to boot up to Windows, I'm assuming your main partition is still good, so what did you do or what happened to cause the second one to dissapear?