I doubt it'd be caused by WinMX personally. I guess it's possible it could be some dodgy software operating on your machine though I'm a bit skeptical of this, sounds a bit extreme, and am more suspicious of the condition of your Maxtor harddrive judging by what you wrote (random data in text files).
I suggest you go about checking the condition of the drive first to try to determine whether it's healthy or not. Grab the 'Powermax' application from Maxtor @
http://www.maxtor.com/en/support/downloads/powermax.htm, stick it on a floppy, and boot your machine from it. I can't remember offhand but the application has options to perform a health check on the drive. It may be worth performing a full READ-ONLY surface test (could take a long time to complete) to be fully sure.
If you get to the point where the data on the Maxtor HDD is FUBAR I'd recommend using the Powermax program to perform a low level format to recertify the entire harddrive (rewrites the entire drive to zeroes) on the offchance it can be brought back to life.
Good luck, and if you are at least able to read from the drive and have anything important on it, get it copied off ASAP.