Strange that connecting the player would crash your whole PC rather than just refuse to communicate with it. Also, unfortunately the T20 is the least popular of the T-series players so there has not been much discussion here on that one.
Some suggestions though:
1. iRiver Plus 3 is for UMS players. If the T20 is MTP it won't work with iRiver Plus 3. T-series players with MTP firmware are recognized on systems with XP SP2 and Windows Media Player 10 installed. If MTP the player may not connect properly with the driver installed.
2. If the T20
is UMS: It's possible the driver file may have gotten corrupted during download. Try deleting it, then download a fresh copy and again put it into the correct folder in Windows Explorer.
If neither of those help you might try looking here for other ideas:
This thread entitled "Computer won't recognize my T20":
Computer won't recognise my T20
This thread started by Ted Yo specifically regarding connection problems has helped many when their players refused to connect properly. The thread starts as a poll, just scroll down to the first message and read through the thread for possible solutions:
Device enumeration problems (but not what you think)