Hi
I have a t22 which i wanted to upgrade the memory on(1 x 128mb pc100occupying 1 of 2 slots existing). The two slots are back to back, meaning the only way I could get a second module in was to turn it upside down, meaning the black chips are facing down, as opposed to facing up on the other (is this right?). I bought and installed a second 128mb pc100 upside down.
When I power up, I get the safe mode selection screen, then it goes to the normal thinkpad startup screen but then i get a blue screen saying something about encountering problems (doesn't stay visible long enough to read), then it returns to the safe mode screen again and so forth indefinitely.
Any advice would be gratefuly recieved.

Hello jdncoke08, welcome to PCHF.

Sounds like you have installed the chip correctly, but either the chip is not compatible, or faulty. Check for compatibility between the other chip by removing the original chip, and see if you can boot normally using the one.

As for checking for memory problems, you can use memtest.

- If you have a floppy drive and a spare floppy disk, please download: http://www.memtest86.com/memtest34a.zip

- If not, please download, unzip and use nero to burn this image: http://www.memtest86.com/memtest86-3.4a.iso.zip

Reboot with the CD/Floppy in the drive and start memtest. This will ensure there are no problems in memory.

Tried the new chip alone and just got a black screen; guess i bought the wrong chip. Maplin said as long as it was SDRAM and PC100 it should be ok. £20 quid wasted, I have seen the sites where they match your laptop model to the RAM, should I use one of these and just buy some more?

You could do, but just make sure the RAM that they gave you is not faulty (if possible) using memtest. It's also possible that the slot itself maybe faulty, so it maybe worth trying that new one in the other slot to be sure.

Thanks again, will do the test and post back. The new chip says PC 100 (2) 128MX4; The original says PC100 128MB; Is this significant?

Not sure about the MX4, but like many laptops, the Thinkpad T22 is very specific in it's memory requirement, up of 512mb, PC100 SDRAM 144pin SODIMM, Non-ECC and Unbuffered. If it's not what they gave you, or doesn't work, I would blame the guy that sold it to you and take it back, as it's a little bit more than just "SDRAM and PC100 and yep, that will work". Some people will sell you their grandmother given half the chance!

EDIT: Marked as Answered.