I bought XPS 15 L502X almost 4 years ago. It had 500 GB HDD. So I burnt 2 Dell Recovery DVDs. Also created ISOs from them. I have both DVDs and ISOs. Then to free up the space I deleted its recovery partition. That saved me some 8 to 10 GBs. For last couple of years I am running Ubuntu. Now that Windows 10 is free upgrade, I am thinking to install original Windows 7 from recovery disks. However my old DVD reader on my laptop is not functioning properly. So am not able to use those recovery DVDs. Now what I have left is ISOs. Can I burn two recovery ISOs to bootable USB? Or is there any other way to get my old factory Windows 7 back ?