I would start by going here
ASUS - Notebooks- ASUS K50IJ
Catch up all drivers to most current version available for your product. Additionally your BIOS version is a bit dated
Version 207 05/08/2009
There have been six revisions since that version so you may want to consider catching up to the latest (according to their note version212 added Win7 Support).
After which I might suggest considering updating
Link Removed, after first checking your system using this
UPDATE READINESS TOOL.
Download and install the correct system readiness tool prior to installing SP1.
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Update these two drivers
L1E62x86.sys 6/11/2009 Atheros AR8121/AR8113/AR8114 PCI-E Ethernet Controller...