fresh as in you formatted the hard drive during the install?
or fresh as in you kept all the old stuff and threw windows on top of the old?
My canned random reboot Rant
Random reboots are usually caused by the PSU, the RAM or software AND in that order of likely-hood.
PSU - If you can borrow/swap a PSU for testing. sibling/friend you can swap out the PSU and each system will be testing the other.
RAM - run the system with one stick of RAM see if stability returns if not Test all the RAM with memtest 86 for five passes or overnight. if you get no 0 errors after more than five passes the ram is good. with the random reboots I would suggest running this test after the PSU swap or after the PSU has been cleared.
Software - Drivers or other issues can cause reboots. Boot to a linux distro on a USB drive. mint linux will boot to memtest86. you can run the OS from the USB and await reboot.
end canned rant
you said reboods when idle AND cannot download and will not uninstall. this decouples the restarts from the PSU as the culprit, the PSU would not stop the downloading or the uninstalling which leaves windows itself (software) or the RAM has an issue. its worth testing the RAM at any rate.