New RAM problems

Hi everyone, seems I’ve made a blunder when buying new RAM as after putting it in windows will not start.
I did a crucial scan and they recommended:
1GB, 184-pin DIMM, DDR PC2700, CL2.5, Unbuffered, NON-ECC, DDR333, 2.5V, 128MegX64

I thought i’d be clever and get the following off Ebay:
1GB PC2700 DDR Memory RAM DDR333 non-ecc, cl2.5, 184pin 128x8

All the spec seems to match apart from the 128X64 / 128X8.
Also the existing RAM was PC2100, although Crucial says that’s ok.
It’s a HP desk top Pavilion 433 UK with two memory slots (max RAM 2gig), I currently have 2X256 MB. I tried putting the new 1 gig in on its own and next to either one of the existing, still get the start-up screen. It slotted in fine.
Any ideas? :confused

 

Sorry everyone... just done a few hours of research and discovered that i bought high density ram(128x8) from ebay... didn't find out enough about it, my standard hp machine only accepts low density... hope i've not wasted anyones time.