Upgrading RAM

I am working on an older system that still takes the old SDRAM. I picked up a new 512 stick today and when I try to install it, it won't seat right. It will get one side in but not the other. Then when I pop out the side thats in the other will fit. Everything lines up and when you look at the old RAM (which pops in and out with ease) all the holes line up. Only thing I can think of is that I bought PC133 and the old stuff is PC100 but I can't see ANY physical differences and I have always heard that even if you install PC133 on a PC100 system the mobo will just only run it at 100mhz. Any hints, tips or tricks?

 

All I can say is install it straight down as when you put one end in, the opposite end gets a tad longer because it's on an angle.

 

So there is no physical difference between PC100 and 133?

 

No, there shouldn't be.
What could be a problem is where the 'bridge' is on the ram, make sure it alignes correctly with the 'bridge' in the RAM slot.
This wiki is a good info source.

 

I have no idea what the deal is but I am afraid if I put any more pressure on the mobo it is going to break. I am trying to put it in evenly but it just doesn't want to go for nothing.