Not able to open Network connections and System properties

i have a laptop with configuration core duo 2.0(T2450) ghz, 512+2 Ram

(667mhz) 160GB hdd. As a factory product it came with vista home basic. I

installed xp proffessional as dual os. Both were working fine. 3 days before

i have bought ram to upgrade but that is bad system was giving plenty of

errors so i replaced the old Ram. after that if i connect the network cable

before starting the system it is working wine. if i start without network

cable connected system is neither opening the network connections nor the

system properties. i tried the following

* Restored from the restore points before upgrading the ram

* Tried to reinstall the LAN Driver it's not able to update the driver

* Tried to update windows xp but it's not responding and staying the step

Collecting informations for ever.

so please help me