Machine details(let me know if you need more information):
OS: windows 7 64bit (lastest version)
Processor: intel core i5 (2nd gen)
Graphics: AMD Radeon HD 6450 (drivers are up-to-date) 2GB VRAM
HD: 1TB total, 4 partitions, 501 GB free room in the windows7's partition
Again, this problem started with minetest's lastest version. the previous ones run just fine. Any idea what caused this? Thanks in advance.
The solution(?): start menu > all programs > accessories > RIGHT-CLICK the command prompt to RUN AS ADM > type SFC /scannow and hit enter.
The engine folder icons are now full of padlocks, but the thing is running, so...
Alternative: try placing the Minetest folder outside the desktop and its subfolders.
Anyway, I would like to thank everybody who replied and here for taking your time to see what you could do to help me. Thank you! ♥