RAM Question

[PGTBeuregard]

I recently received an old computer from a relative, and so I took out the Motherboard, since I've replaced most of the hardware in my Computer except for that, anyways.
Motherboard Specifications, A8N-LA (Nagami2) Compaq Presario Media Center SR1950NX Desktop PC - HP Customer Care (United States - English)
New Board specs for reference

So I got 2 sticks of DDR PC3200 184 Pin 400mhz, what the specs say is compatible, but I attempt to fit them in, and they wont work. So I checked the old ram from the MB and it said DDR PC3200U 184 pin 400mhz, What does the "U" Mean? And Is it Incompatible? Where can I Buy PC3200U RAM at?
Btw, Lol at super upgraded budget Rig from 5 years ago

FRYS.com*|*PATRIOT
Or Maybe i'm fail and I don't know what DIMM was, Fix'd?
Link:RAM I bought, not DIMM

 

[Yami]

They look like they should work - the RAM is correct according to the mobo's specifications.

Can you be more specific about 'they wont work'? Does the machine not boot, or do you get an error, etc.?

 

[PGTBeuregard]

They look like they should work - the RAM is correct according to the mobo's specifications.

Can you be more specific about 'they wont work'? Does the machine not boot, or do you get an error, etc.?

The RAM sticks will not fit into the slots well, they are the correct length and everything, but they do not go deep enough into the slot, so the things that look like this I''' wont secure them in, and I've tried pressing them in with a medium/hard amount of force. I Also compared the new sticks with the ones previously in and the new ones are about 1-2mm shorter than the old ones.

Edit: YES!, I fixed it, I was able to fit the ram into the slots by pressing each side one at a time, thx for the help, but FIXD!

 

[Muffin Man]

they can be different heights.

are you maybe installing it backwards? make sure the notch on the ram stick lines up with ram slot. when it's lined up, insert it into the slot. the little clips or latches on the sides should lock in place as you push it in.

example