My computer restarts

Hello,
plz would you help me............ i have a acer laptop namely, acer travelmate 4730......it has been some 1 month i bought it...... it did not have problem then.but last week i iinstalled windows 7 here in my laptop since then my computer restarts often. even when i am doing a important job. iseached for virus but no virus were found. and in that ssame case my microphone doesnot work, noan any hardware problem only software problem.....................plzzzzzzzzzzzz would you send me your sayingi in my problem in my email............plzzzzzzzz i would be grate ful for that............