Hi,
If your computer turns off suddenly when you open two or more websites, you might wanna check the following:
1. Scan for virus on your computer.
2. Try to boot into Safe Mode with Networking (you need to press F8 continuously upon boot-up and choose Safe Mode with Networking) and try to check if issue still occurs.
3. If Step 2 fixes the issue, try to disable start-up items that might be causing the issue, step by step guide
here.
4. If Step 2 fails and gives you the same issue, you might wanna try doing a System System Restore (if it was working before, step by step guide
here or factory restore (you need to press F2 upon boot-up for built-in recovery - backup important files first before proceeding)
5. If all of the above fails, check if the computer is overheating. If it does, you need to have the computer serviced. Call Lenovo Customer Support at 1-877-453-6686.
Additional Troubleshooting Steps can be found
here.
Cheers.