Hi Sandy. I'm Greg, an installation specialist, 10 years awarded Windows MVP, and Volunteer Moderator, here to help you.
You're right that a Celeron is a weak processor. I'd observe how much RAM is being used vs. CPU as it may be too weak a processor to even use all the RAM.
1) What can make up for it some is the quality of the install. What we have found is that in Windows 10 what matters most is the quality of the underlying install, the same reason enthusiasts have never run Factory or Upgrade installs because they know there would be endless issues.
For example there have been zero return problems by those who follow the gold standard Clean Install here:
http://answers.microsoft.com/en-us/windows/wiki.... It is better and faster than any previous version of Windows, and a better install than any amount of money could buy. So when you get time I'd study over that to see if it's something I can help you do.
2) The Display driver is so important here that merely updating it is sometimes not enough. So let's try everything possible to get it working correctly:
First make sure you have updated the Display driver from the PC or Display adapter maker's Support Downloads web page for your exact model number, HP Serial Number or Dell Service Tag - from the sticker on the PC.
While there check also for newer chipset, BIOS/UEFI firmware (very important), network, sound, USB3 and other drivers, comparing to the ones presently installed in Device Manager reached by right clicking the Start Menu.
If this doesn't give you the latest or ideal driver for what you need, compare it to the driver offered by the Intel driver update Utility here:
http://www.intel.com/content/www/us/en/support/...
or the Nvidia Update utility here:
http://www.nvidia.com/Download/Scan.aspx?lang=e...
or the AMD autodect utility here:
http://support.amd.com/us/gpudownload/windows/P...
For Display issues one fix that is working is to Roll back or Uninstall the Driver on the Display Device > Driver tab, restart PC to reinstall driver.
You can also try older drivers in Device Manager > Display device > Driver tab > Update Driver > Browse > Let Me Pick.
Then you will know you've tried everything in addition to Windows Update drivers.
Adjust the screen resolution until it fits and looks best at Settings > System > Display.
I hope this helps. Feel free to ask back any questions and keep me posted. If you'll wait to rate whether my post resolved your problem, I will keep working with you until it's resolved.
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