node.js - can't get mongodb to work, may have installed wrong?

I guess this is a shot in the dark since there's not a lot of specific code I can show you...

but I'm using node and trying to use mongodb, however I can't get mongodb to connect. I've tried a couple of tutorials that should pretty much work out of the box. in several cases pages that don't seem to have any immediate reference to the database will load ok. For example, a 'posts/new' page will load. but '/' which likely makes reference to showing posts, will just hang silently (the browser shows page loading).

If for example I got so submit a new post the browser hangs and in the terminal i get:

Express app started on port 3000
Error: Invalid ObjectId
at Function.fromString (/Users/xxx/Node_projects/noobjs/node_modules/mongoose/lib/drivers/开发者_JAVA技巧node-mongodb-native/objectid.js:27:11)
at ObjectId.cast (/Users/xxx/Node_projects/noobjs/node_modules/mongoose/lib/schema/objectid.js:99:16)
at ObjectId.castForQuery (/Users/xxx/Node_projects/noobjs/node_modules/mongoose/lib/schema/objectid.js:133:17)
at Query.cast (/Users/xxx/Node_projects/noobjs/node_modules/mongoose/lib/query.js:249:32)
at Query.findOne (/Users/xxx/Node_projects/noobjs/node_modules/mongoose/lib/query.js:851:10)
at Function.findOne (/Users/xxx/Node_projects/noobjs/node_modules/mongoose/lib/model.js:714:16)
at /Users/xxx/Node_projects/noobjs/routes/articles.js:13:13
at paramCallback (/Users/xxx/Node_projects/noobjs/node_modules/express/lib/router/index.js:259:7)
at param (/Users/xxx/Node_projects/noobjs/node_modules/express/lib/router/index.js:241:11)
at pass (/Users/xxx/Node_projects/noobjs/node_modules/express/lib/router/index.js:253:5)
GET /article/new 500
GET /articles/new 200

if it helps at all, here's the package.json for the tutorial app used above:

{
"name": "noobjs"
, "description": "A demo app in nodejs illustrating use of express, jade and mongoose"
, "version": "2.0.0"
, "private": true
, "author": "Madhusudhan M S (http://twitter.com/madhums)"
, "engines": {
  "node": ">= 0.4.10"
}
, "dependencies": {
  "express" : ">= 2.3.12"
, "jade"    : ">= 0.12.4"
, "mongoose": ">= 1.4.0"
, "stylus"   : ">= 0.13.7"
, "express-csrf" : ">= 0.3.3"
, "gzippo"   : ">= 0.0.4"
, "express-messages" : ">= 0.0.2"
}
}

Also when I do ./mongod from the command line i get -bash: ./mongod: No such file or directory. Anything else I try from the terminal or browser doesnt seem to communicate with mongodb at all.

Let me know if there's anything I can do to diagnose/change my installation.

Step 0: ensure that MongoDB is running ps -ef | grep mongod. If it's not started, check the log file for the reason it failed.

Step 1: ensure that you can connect to MongoDB from the command line.

Step 2: check your connection method, there are several ways to do this, but ensure the you have the correct servername:post/dbname

Here's a blog post I wrote. That walks through a simple setup with Node.JS + MongoDB + Cloudfoundry. The simple setup works locally and on Cloudfoundry, so you should be able to ignore the Cloudfoundry steps and still get something working.