MaxWonga, I had this exact problem with my dell c521.
it would not load windows with the 4 1gb sticks.
Load it up with 2 of them in slot 3 and 4.
then go to - "Try this, go to start->run->msconfig
Go to the BOOT.INI TAB.->advanced"............ and untick the "max memory" box and the field will be blank.(previously showed 2048)
turn the pc off, stick the other 2 x 1 gb sticks in and fie it back up.
sorted, boots up on the 4gb
This actually worked for me. I've been fooling with this for almost 2 weeks without success. I would never have thought of this method. Many thanks.:bounce: