How to delete a computers hard drive?

I got a new computer and I left for a month for vacation I left my computer at the house and my 14 little brother started going on live stream websites he went to a website to download minecraft for free and now I get pop ups and stuff on my desktop I think it may have a lot virus and it's I bit slower any help?

Try this.

Boot up in "Safe Mode with Networking" - Go to malwarebytes.org, download, install, update and scan with Malwarebytes Free Version. Do the same with Spybot Free Version from safer-networking.org and again with lavasoft adaware free from lavasoft.com.

You may need to run all scans a few times and let Spybot run before startup to clean out everything.

If your pc is win 8 or 8.1 do a factory reset it take 6 hours / than you will have to do all your updates again ;next time make yourself only as administrator ( n password the log-on ) . I never leave my pc to where someone can get into it i take the battery out and the charger

Pall Mall is wrong or has an amazingly slow computer. I have Windows 8.1 and I just did a factory reset. Took less than 10 mins.

Anyway to do a Factory reset with Windows 8 or 8.1
Hit Windows key and "I"
Change PC settings (at the bottom)
Click Update and Recovery
Then hit Recovery

With Windows 7
When turning you pc on, Hit F10 or F11 (Or depending on you pc could be different)
Then hit Factory Reset!

Both of these will uninstall EVERYTHING and re install windows. (With out disc) so with a USB back up anything you NEED!

You don't Delete a Hard Drive.
You UNINSTALL programs that were installed.

Go to Control Panel > Programs > and uninstall what you don't want.

Also create a New User Account for yourself. With a Password.
Log on to that account and delete the old one.