iMac keeps freezing / turning off

Hi all,

System details as follows:

iMac 17inch Late 2006

OS X Lion Version 10.7.5

Processor 2GHz Intel Core 2 Duo

Memory 3gb 667 MHz DDR2 5DRAM

110gb free of 160gb

I was given this machine a few years back by my brother in law - i now have it set up to run / stream to my Apple TV and do a bit of work on.

I have a 2TB hard drive connected to it which contains about 1.5TB of Films, TV Shows, Music and Pictures.

The iMac keeps freezing / restarting itself and different points - mainly when i am on iPhoto / iMovie.

I have just disconnected the hard drive and it seems much better, but i cannt use it like this (much). Update - it's just frozen a couple of times without HDrice connected!!!!

My main question is - have i just got too much stuff for the iMac to handle and if so is there a way around it?

Also is there any way to give it a general spring clean / tidy of unwanted files etc?

Any advice welcomed.

Thanks in advance.