Welcome to the forums!
If I understand correctly you are not able to connect to your SQL Server after your restore the system. According to http://www.5starsupport.com/faq/xp-system-restore.htm#1-5 windows system restore will leave your installed programs intact. Was SQL Server 2008 installed before, and more importantly after SQL Server 2008 installation did you Create a restore point!!
Can you please post the error message!! So that we can understand the scenario better!!
Hemantgiri S. Goswami
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"Humans don't have Caliber to PASS TIME , Time it self Pass or Fail Humans" - by Hemantgiri S. Goswami
http://hemantgirisgoswami.blogspot.com
http://forums.surat-user-group.org/

Disclaimer: This post is provided as is, for the sake of knowledge sharing only.