By delete everything off it you mean Formatted it don't you?
Sounds like you formatted it in the wrong format. Mist cards needed to be in Fat16 or Fat32 but XP/VISTA defaults to NTFS
Sandisk have a lifetime warranty, i always use Sandisk as they are the most reliable.
As long as there are no files you need to recover try reformatting it in a camera, normaly does the trick. Sandisk Pro used to come with recovery software if you need some try an find it on somones card or off Sandisks web site
DinoHunter (still no nVidia compo voucher!), CPU/GPU Benchmark, DarkFish Encryption DLL, War MMOG (WIP), 3D Model Viewer