Solution Ubuntu 8.04.1 freezes or locks up

Three problems are often noted:
System freezes often running Firefox 3 with Flash?
I tried this, gave some results but didn't fix the problem totally.
Deinstall completely all Flash components not only Flash, but also libswfdec and the swfdec-mozilla plugin with Synaptic packet manager.

Go to http://labs.adobe.com/downloads/flashplayer10.html
and download Flashplayer 10beta or search a newer one when available...
Install it by doubleclicking the install file.
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This problem also may lead to unwanted closing of Firefox:

Aim:

If Firefox 3 closes down each time you visit certain sites, it may be because you have two flash movie players installed in Ubuntu. Uninstall one flash player to stop Firefox 3 from closing down.

How to stop Firefox 3 from closing down on some sites:

Go to System > Administration > Synaptic Package Manager and search for "flash". Check if both Gnash and Adobe Flash Player plugin ("flashplugin-nonfree") are installed. If this is the case, mark one for complete removal and click on Apply.

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Edit: This doesn solve the problem totally as after 10 minutes of Youtube the system froze again, but otherwise the problem is less severe...

Edit2: When I try to write a comment in Firefox 3 the system freezed too today.
Strange that even the SysRq+ alt +b didn't work to reboot..

Second cause: wireless connection interfering

Edit3 and temorary solution: I read that it might have something to do with my wireless and non wireless connection interfering with each other.
Use the command to find out what is working on your pc:

ifconfig

In my file /etc/network/interfaces I could only find:

auto lo
iface lo inet loopback

So I added the lines:

auto eth0
iface eth0 inet dhcp

wlan0 wasn't mentioned in my file.

How to edit your interfaces file:

sudo kwrite /etc/network/interfaces

( KDE )

sudo gedit /etc/network/interfaces

(Gnome)

sudo gedit /etc/network/interfaces

(XFCE)

sudo nano /etc/network/interfaces

(all ,save with Ctrl+ O and Ctrl + x quit).

Cause 3: A restricted ATI Video Driver

Edit4: Another reason that was given for lockups are the restricted ATI Video Driver.
I used the following tutorial to updat this one following method 2.
It looks far more complicated than it is to follow these instructions:
http://wiki.cchtml.com/index.php/Ubuntu_Hardy_Installation_Guide

source: http://forum.ubuntu-nl.org/topic/24231