It constantly changes. But I remember it was once PUREBLOOD in the Chamber of Secrets
In Harry Potter and the Chamber of Secrets the password was pure-blood.
Draco Malfoy
In "Harry Potter and the Order of the Phoenix," the Slytherin common room is located in the dungeons of Hogwarts, beneath the Black Lake. To access it, students must enter through a bare stretch of stone wall and provide a password. This leads to a door that opens into a green-lit, luxurious room decorated with dark furnishings, characteristic of Slytherin House.
Go to the room with the Slytherin portrait while wearing your invisibility cloak. You'll see two Slytherin students use the passageway, thus revealing the password to you.
parseltongue,
Slytherin.
Slytherin
The Slytherin common room was through the dungeon, and behind a stone wall.To get into the Slytherin common room, you need to have the password. In Harry Potter and the Chamber of Secrets, Harry and Ron entered the common room in disguise. During that time period, the password was PUREBLOOD.However, we know that at least in Gryffindor, the password was constantly changing. It is pretty safe to assume that Slytherin would change theirs frequently as well.
Draco Malfoy won't give you the password. To get the password, go to the portrait while wearing the invisibility cloak.
Harry particulary hates Slytherin.
No, James Potter was in Gryffindor house. Harry's mother was also in Gryffindor.
Wear the Invisibilty cloak (get it from the Gryffindor bedroom trunk) and go to the portrait at the bottom of the Grand Staircase. Follow the Slytherins. They will say the password.