mouse problem (mx510)

I've big problems with my MX510, although I've some ideas about the cause, but I need your opinion, maybe some of you had the same problems yet.


So, the problems:
1. Sometimes the mouse turns on and off

2. Sometimes the mouse go crazy: you don't grab/move the mouse, but the cursor is moving randomly, and opening, closing (clicking) randomly - this is usually some hours after turning on the pc

3. The sensitivity decreases to half as big (just simply or after this "crazy" event) - in the windows control panel it's always on the maximum, and after it decreases to the half in control panel it's still on the maximum. For example I start a war with /sensitivity 1.2, and i need finish it with 5.0 to have the same sensi what i used in the beginning, and in windows (logitech control) no change, so there it's still (always) on the maximum.


Results:
1. Need wait, and sometimes it never turns on and i need restart my pc.

2. More disturbing. For example it closes the webpages, mirc, documents etc what i opened. In ET i get a kick for excess flood if this crazy thing happens!

3. Can't play, coz it's very disturbing if the sensi decreases ingame. I cannot raise more in windows (coz it's aw on the max.), i can raise only ingame. Or pulling out and pluging in the mouse, this solve the problem usually.


More info:
- all the same i use it on ps/2 or usb, problem the same
- i'm using it now in ps/2 before this i used it in usb @ 125 and 500 hz
- i just formatted pc, reinstalled windows, it doesn't help
- no virus on my pc
- my brother tested the mouse on his pc for an hour, but didn't find any problem


My ideas:
- problem with the mainboard (after hours?)
- problem with the cooling
- problem with the mouse (but only after hours?)
- problem with the power supply (after hours?)

I hope you could help me somehow. Tnx for your ideas anyways.