Imac will freeze unexpected

Hi together
have an I Mac with an Intel Dual Core 2.16, 4 GB Ram 250 GB HD with OSX 10.6
After installing Parallels Desktop i put on a Windows XP with Service Pack 3.
then i installed a Photoshop CS2 and Silverlab order Managment for a Copal DPB 6000 Printer. the Software needs a dongle. I also use an USB hab, cause i use a card reader and the Printer also on a USB port.
Keyboard and mause are cordless.
If i start the windows site in 50 % off strting the mouse and the keybord will not work also on the Mac ste too. So i have to do an cold starting again. Can anybody help me to avoid the freezing? does anybody Knows what i have to do to avoid this issue?
Paralles presets are default.
Best regards
Hubertus