my FAT32 drive is not seen by unetbootin

Hello,

I'm a beginner in linux, and I want to install ubuntu on an old computer, to replace windows XP.

I have a usb drive sandisk, like this one : http://www.amazon.fr/SanDisk-Cruzer-Fit-Cl%C3%A9-SDCZ33-032G-B35/dp/B00812F7O8/ref=sr_1_2?s=computers&ie=UTF8&qid=1421500818&sr=1-2&keywords=sandisk+32Go+cl%C3%A9+usb
I formated it in FAT32, "fast" or not, and even try NTFS format.

The computer is a Powernet "N09 - 00310PWN", running on a windows xp OS

The problem is that the unetbootin program cannot see the usb drive. It launches normally, but it can't see the usb drive. I acn select my hard disk, but not the usb drive.

I redownloaded it several times, the same problem appears.

I download an iso file to use the iso method, but it doesn't change anything, it still don't see my usb drive.

The last thing I do is to set unebootin on an other computer, but the installation failed : I believe the unetbootin programs does detect what is the exact configuration and then set the ubuntu setup for the computer which runs unetbootin...

Maybe with an iso file I can set my usb drive for the old computer ? Does the install will fail and it must be run on the computer that i want ubuntu installed on ?

Is the problem the huge size of my usb drive ?

Or the age of my computer ? should I choose another linux distribution better for old computers ?

Any information is really welcomed

(Sorry for my english, I'm not an expert in this language)