i had upgraded memory on my machine HP pavilion 754n came with 512 added a 1gb for total of 1.5 gb. had to replace hard drive last week nothing would load until the 1gb was removed,in searching found the motherboard supposedly only supports 1gb max. machine ran fine for almost a year with the 1.5gb installed. my question is should i could i reinstall the 1gb and what might it do th the machine in the run?

btw when instelled the machine would show 1.5gb ram so does this machine actually support more than 1gb ram/

Ok, I am looking at the breakdown of your computer:

http://h10025.www1.hp.com/ewfrf/wc/document?docname=bph08026&lc=en&cc=us&dlc=en&product=296688&lang=en

I notice it states "HP approved maximum memory 1 GB (requires replacement of the installed DIMM(s))", which would say that HP only approves 1GB max RAM, but it may actually support more than that.

The motherboard is MSI model MS-6577. You can probably download BIOS and driver updates at the www.MSI.com.tw website. I will look into other stuff with that in a bit (I'm heading out for food in a sec).

The Intel 845G chipset support dual channel RAM if I remember right, so you would get max performance from your system by filling both slots with equal sized sticks (both 512 or both 1GB).

It doesn't make sense why this would happen after a hard drive swap, really.

Let me get back to you in a bit. Meanwhile, if it's of any interest, here is a link to software and driver downloads for your computer from the HP site:

http://h10025.www1.hp.com/ewfrf/wc/softwareCategory?lc=en&cc=us&docname=bph08026&dlc=en&product=296688&lang=en&

Okay, after reading around, this is what I'm going to suggest:

Remove the 512MB stick. Pop in the 1GB stick as the "0" slot or "A" slot. Boot up. Does it work? If yes, try to add the 512MB stick. Does it work?

Given that the manuf'er rates the system as 1GB max RAM, I hate to be the guy that says "listen to the manufacturer!", but it might be best in this case.

I can't explain to you why it was working before. I know that HP sometimes adds a "tatoo" to their systems that won't let you upgrade components or use rescue disks unless it is present - I think this is on the mainboard, but I am not 100% on that.

The only other alternative that I see is to find a community of people who hack the older Pavilions and eMachines and try and find someone who has released an unofficial BIOS revision for your system, and try that out.

I would also suggest downloading the most recent BIOS update for your computer and flashing it: http://h10025.www1.hp.com/ewfrf/wc/softwareDownloadIndex?softwareitem=pv-17635-1&lc=en&cc=us&dlc=en&product=296688&os=228&lang=en

Maybe someone else might have more experience with HP computers - if this was a Dell, I could give way more support. Their systems are a lot more streamlined, easy to use, and easier to support if you've used them long enough.

I recently upgraded RAM from 128 to 640 (added one 512 stick) in my Wally world special Compaq Presario S2040WM. Made a WORLD of difference.

Because the RAM sticks were different amounts, I was unsure which to put into which slot. An online HP tech advised me to install the larger RAM stick into the DIMM slot closest too the MB ("0" or "A" slot). That meant removing the original 128 stick, installing the new 512 into that slot, and then putting the old 128 into the 2nd, previously unused slot.

I don't know if this is the case with your system, but just adding my $0.02 and experience.

thanx for the info unsure what im gonna do right now may just wait and buy another 512 and install in future but will check out all optins in the links provided