Windows XP starting problem

Windows XP was running normal and perfectly stable (over
one year) until I decided to add 512mb ddr, ups and 120gb
hdd. I've installed windows XP on second partition of
that new disk.

Now, my problem look like this:
When I turn on my computer, Windows doesn't start - only
black screen waits me. When I restart, it can be ok, or
it can be like this: Windows XP starts randomly (when I
restart it, cca. every second or third time), it starts
with 8bit color, and resolution cannot be changed. I've
tried everything: (re)installing new and old drivers for
my geforce4 mx 440, installing monitor drivers,
installing generic Microsoft drivers for my graphic card -
everything that crossed my mind. But still it
starts - one time normally, then on 4bit color (which
cannot be changed in display properties).

Thing that's confusing me is the fact that everything
worked normally in my previous XP installations, for over
a year, and now it's problematic.

I tried to do everything having SP1, without SP1, with DX
8, with DirectX 9, everything.

Anyone have idea how to solve this?

Thanks in advance.