I have a PNY Optima Attache 4GB flash drive and Vista only recognizes it about 25% of the time. Usually, when I put it in, the green light flashes and the "safely remove hardware" icon shows up in my task bar, but the drive doesn't show up under "my computer." On occasion, however, it works like normal.

Hello Adigiorgio!

2 things to check ----

1) Device Manager - does this device have an Exclamination when it is installed?

right click on My Computer -> Manage -> Device Manager

2) The device might be getting a drive letter assignment conflict. Could you check Disk Management for issues regarding the drive assignment?

right click on My Computer -> Manage -> Disk Management

You should be able to identify the device easily and make assignment to an open drive letter.