How do I get to the second level of Arachni's Haunt?

I have a quest 'scrambled reinforcements'. The quest doesn't tell how to get through this place.
Made it through level 1 to a portal that is blocked by a door.
Now what?

Never had that problem, but I'm willing to bet you can't go down to level 2 without killing all the Spider Matriarches. Done that?

Also, there should be a key that drops.

http://guildwars.wikia.com/wiki/Arachni%27s_Haunt

Hope it helps.

Keep on going. You have to find the "boss key" and "boss lock," as with most/all dungeons

Look for stacks of spider eggs to burn. Burn one stack at a time as spiders spawn with each one set afire. First area after poison corridor, there are two stacks. When you set the second afire, the Matriach will appear.

Second set is in room before last webbed gate. As soon as you kill the Matriach, the dungeon key will appear on the ground in front of that gate.

I'm standing there right now waiting for my guildmate to not be afk.

There are times I have done that dungeon and not had the Matriarch spawn. I went back to the first set of eggs, and realized it was a MAJOR delay in the spawn. Sometimes you have to move around the area enough to cause the spawn to occur. Not sure why this happens, but I have seen it happen several times.

Maybe I asked the wrong question. The only reason that I entered Arachni's Haunt, was that I thought completing Arachni's Haunt would add points to the master of the north title. Is that true?
Must the scrambled reinforcements quest be accepted to complete the Arachni's Haunt dungeon?
Will the scrambled reinforcements quest prevent completion of Arachni's Haunt?

At some point, Commander Hixx, Hudd, and Vask were added to the party as allies. Is having these allies somehow preventing completion of Arachni's Haunt?

There are five things listed for the scrambled reinforcements quest.
Help Hixx and his troops secure Arachni's Haunt.
Destroy 3 spider matriarchs.
Kill Arachni.
Use the asura flame staff to burn through the web gates.
Use the asura flame staff to set ablaze the egg sacs.

These five items are all still active, but there's no green arrow indicating where to go. Is a malfunction preventing scrambled reinforcements from working?

The map shows that I'm currently in Arachni's Haunt. I'm in an area with a portal to the northwest. A collector, Dagnor Grubeater, is on the other side of a wall to the east. There's a closed door at the portal. Is acces to Arachni's Haunt blocked? Is there a way to unlock access to Arachni's Haunt? Is there a place in eye of the north where access is explained? Is this Arachni's Haunt not working properly? Does Arachni's Haunt ever work properly? How often does Arachni's Haunt work properly?

Is it possible to get 10 master of the north points for Arachni's Haunt? That's all I want.

Using "Scrambled Reinforcements" is how you complete this dungeon.

Spider Matriachs are spawned when you burn the last of each "spider eggs" in an area. There are two such areas on Level One. If you haven't killed two Matriachs by the time you have reached the Dungeon Lock, you must go back and recheck the first "spider eggs" area. The Dungeon Key appears on the ground in front of the last webbed gate you burn on Level One only after killing both Matriachs.

The third Matriach is on Level Two.

The portal you are facing is the door to Level Two and requires the Dungeon Key be placed in the Dungeon Lock to open.

this has happened to me the Spider Matriachs would not spawn unfortunately i had to restart and do it again

Answering the three questions you listed at the top of your newest post:

1) Yes. 10 points for first completion in NM, 20 in HM.
2) Yes, the doors in the dungeon won't open without the quest (or so I've read, never been in without it)
3) No, it's required.

Darcy explained it pretty well, but if you're still confused, basically go around the first level, find stacks of eggs, burn them with the Asura Flame Staff. Kill the boss that spawns after the whole collection is burned. Should be two sets of those eggs. After doing all that, there should be a key that spawns to unlock the door to level 2.

If you're not sure where to look for the eggs, follow Isaac's link.

Yep, Definately need dungeons for the Master of the North Title. Yeah burn eggs to get to the bosses. Kill all the bosses from burning the egg sacks. and your good to go.

How often is Arachni's Haunt broken?

Never been broken for me, and I've completed it many times on several different characters. Only problem I have seen is the delay in the Matriarch spawn. It spawned, but was delayed, and I had to explore the area around the eggs to finally get it to show up.

All dungeons require a quest to be able to complete them. Scrambled Reinforcements is the one you need for Arachni's Haunt. The 3 Asura guys who join as allies are part of the quest.

As noted, all dungeons give points to the Master of the North title, and you have to complete them all in both NM and HM to max that title, as well as Vanquishing, quest completion in NM and HM, and Mapping.