Arduino (Leonardo) "destroys" my SD-cards

Hello everybody

I bought a arduino leonardo with a SD-shield last month. I used an example in the ID of arduino.
It worked finde. Now I did a external shield for a pressure sensor.
Now I wanted to test the external shield - but first I did a test like before (Arduino plus SD-shield). Just reading the analogports to write the data to the SD.
That worked (checked the log in the console). After, I inserted the SD-card to my notebook.
I was no more able to read the data. Windows wants to defrag the SD. Okay - can happen. So I started the defrag, but Windows is not able to finish...
I tried some tools - always no success.

Then I took an other SD-card. Was again able to write data from the arduino to the card. But in Windows the same problem >:(
Tried it also on an other PC..

The crazy thing: it worked 2-3 weeks ago perfect - no problems.

Hardware: Arduino Leonardo with a SD-Shield
Software: WIN 10
SD-Card: standard SanDisk SDHC Card (2 Gb and 4 Gb) -> no, the SD-card are not locked!

Thanks for helping me!

Which SD shield are you using? Does it have a logic level converter? A link to it may help.

I use this shield.. Worked a month ago.

=> The 5V-3.3V-voltage regulator works!

That does not have a logic level converter. You are putting 5 volts into the CS and MOSI lines. That can damage the SD card or the Leonardo.