Black Screen Boot or Freeze

I have an HP Pavillion laptop. It's about 5 years old now, but it's served me well without incident until recently. I upgraded the memory (from 2 x 256 to 2 x 512).

Every now and then over the past few months, Windows would show the memory as only 512, or ocassionally fail to boot at all. Swapping the memory into the two different slots usually solved this problem, if only temporarily. Some days Windows would show 512 of ram, others 1024. At least, when first installed it would show 1024 and then after an unknown quantity of time it would fail to recognize it.

Now, having recently cleaned the memory sticks, the laptop does one of two things:

1) It fails to boot up at all (The laptop starts but all I get is a blank screen)
2) It boots up but freezes on login or shortly thereafter (usually the desktop is desplayed, and some icons begin to load, but that's as far as it gets)

Any help would be very much appreciated!

Edit: The laptop now boots properly, and appears to be fine, though it only picks up one of the two sticks of memory. I've been having this problem for many months now, and swapping the sticks between the slots usually fixes it temporarily, as I mentioned.

 

Try it with each stick alone to isolate a possible bad stick. It would be reasonable to suspect the one that you added.

 

In fact I added two sticks, since HP was cheap and claimed the 512 of memory by giving me two sticks of 256 factory with the laptop. So I added two sticks of 512 as the only way to upgrade my ram with only two slots.

Both sticks of ram work sometimes, and don't work others. I know this because Windows DOES initially display having 1024 MB's of RAM, but that only lasts so long.

I've had this problem long before I upgraded the RAM. I just thought that instead of not recognizing it, I simply needed more, so I upgraded, not thinking to check how much of my memory Windows actually recognized.