[Resolved]  HP Pavilion DV2601TU — problem in the laptop

I have bought my HP pavilion dv2601 TU on 1st Nov 2007. after around two days it started giving problem during shut down. it gets restarted during shut down. sometimes it starts doing this two or three times continuously.This problem is not frequent i.e. sometimes the machine shuts down without any problem and sometimes it gets restarted.once in between i did recovery and it worked nicely for around fifteen days without showing any problem but again after that it started showing the problem, i cant recover the system after every 15 -20 days as it requires the reinstallation of all the softwares. I am using the antivirus provided with the machine itself i.e. Norton. i regularly update it and during scanning it is not showing any problem of virus....Kindly suggest me some remedies, as the problem is too annoying.
waiting for earliest reply
Preety