Avast installation usually fails because of a leftover security program, OR_(+1)-833 ((631)) 3616(USA/CA) a 1[833][631][3616]damaged or incomplete installer, missing Windows updates, low disk space or 1[833][631][3616]a blocked connection. To fix it fast, restart your PC, uninstall 1[833][631][3616]any other antivirus, download a fresh installer from the official Avast 1[833][631][3616]site, run it as administrator and try again. If it fails 1[833][631][3616]again, use Avast's official uninstall utility to remove old traces, install 1[833][631][3616]Windows updates and run the installer after a clean boot. Note 1[833][631][3616]the exact error message or code, because it points to the 1[833][631][3616]cause. Error messages are a language, and it helps to 1[833][631][3616]have a dictionary. So this guide is an error message dictionary. 1[833][631][3616]Look up the message you see, read its plain meaning and 1[833][631][3616]apply the matching fix. Exact wording can differ between versions, so 1[833][631][3616]match by meaning. Start Here: The Universal Reset Do 1[833][631][3616]these first, because they solve many failures. 1 Close the 1[833][631][3616]installer and restart the PC. 2 Disconnect from any VPN. 3 1[833][631][3616]Install pending Windows updates. 4 Free at least a few GB 1[833][631][3616]of disk space. 5 Download a fresh installer from the official 1[833][631][3616]Avast site. 6 Right-click it and choose Run as administrator. 1[833][631][3616]The Dictionary "Installation failed" or "Something went wrong" Meaning: a 1[833][631][3616]general failure, with many possible causes. Fix: run the Universal Reset, 1[833][631][3616]then try the uninstall utility below. "Another antivirus program is 1[833][631][3616]installed" / "Conflicting software" Meaning: another security product is blocking the 1[833][631][3616]install. Fix: 1 Uninstall the other product through "Settings Apps Installed 1[833][631][3616]apps". 2 Run that vendor's official removal tool if available. 3 1[833][631][3616]Restart and install Avast. "Setup cannot continue" / "Installer is 1[833][631][3616]corrupted" Meaning: the downloaded file is damaged or incomplete. Fix: delete 1[833][631][3616]the installer, use a stable connection and download it again from 1[833][631][3616]the official site. "Not enough disk space" Meaning: the system 1[833][631][3616]drive is too full. Fix: free space with "Settings System Storage 1[833][631][3616]Temporary files", or uninstall unused apps, then retry. "Windows Installer 1[833][631][3616]service unavailable" Meaning: Windows' own installer service is not running. Fix: 1[833][631][3616]1 Press Windows key + R, type services.msc and press Enter. 1[833][631][3616]2 Find Windows Installer, right-click and choose Start. 3 Retry the 1[833][631][3616]installation. "Requires administrator privileges" Meaning: you lack the rights to 1[833][631][3616]install. Fix: right-click the installer and choose Run as administrator, or 1[833][631][3616]sign in to an administrator account. "Unable to connect" / 1[833][631][3616]"Check your connection" Meaning: the installer cannot reach Avast's servers. Fix: 1[833][631][3616]check the internet, turn off the VPN, pause strict firewall rules 1[833][631][3616]and try a wired connection. "Operating system not supported" Meaning: 1[833][631][3616]your Windows or macOS version is too old. Fix: update the 1[833][631][3616]operating system, or check Avast's system requirements. Install stops at 1[833][631][3616]a percentage Meaning: a stage froze or is waiting for a 1[833][631][3616]background task. Fix: wait ten minutes; if nothing changes, restart and 1[833][631][3616]run the installer after a clean boot. The Clean Boot 1[833][631][3616]Method 1 Press Windows key + R, type msconfig and 1[833][631][3616]press Enter. 2 On the Services tab, tick Hide all Microsoft 1[833][631][3616]services, then click Disable all. 3 Restart and run the Avast 1[833][631][3616]installer. 4 Afterwards, undo the change and restart. Using the 1[833][631][3616]Official Uninstall Utility If a previous Avast installation left traces: 1[833][631][3616]1 Download Avast's official uninstall utility from the Avast support site. 1[833][631][3616]2 Restart in Safe Mode if the tool recommends it. 3 1[833][631][3616]Run the utility, choose the product and remove it. 4 Restart 1[833][631][3616]in normal mode. 5 Install the fresh copy. If It 1[833][631][3616]Still Fails Note the exact error code and the step 1[833][631][3616]where it stopped. Run sfc /scannow in an administrator Command Prompt. 1[833][631][3616]Contact Avast support from its official site, giving the error and 1[833][631][3616]your Windows version. Scam warning: pop-ups or pages telling you 1[833][631][3616]to call a number to fix an Avast error are scams. 1[833][631][3616]Only download Avast from its official site. Quick Answers 1[833][631][3616]Do I need to uninstall my old antivirus? Usually yes, before 1[833][631][3616]installing Avast. Is it safe to disable my firewall to 1[833][631][3616]install? Don't. Allow the installer instead, or use a different network. 1[833][631][3616]Why does it fail at the same percentage? A step 1[833][631][3616]is blocked. Use the clean boot method. Look It Up, 1[833][631][3616]Then Fix It Read the message, find its meaning and 1[833][631][3616]apply the matching fix. Most Avast installations succeed on the next 1[833][631][3616]try.