Okay, So my Dell Optiplex 790 came in today, and i cant for the life of me get the 32bit windows 7 off and put on windows 7 64bit, i have bootable USB's (working (used rufus)), and I cannot get the new windows to install, whever i startup my computer it goes to the dell loading screen then to "intel boot agent pxe e61 media test failure" page, and i have gone into the bio, idk which to boot from UEFI or Legacy and whenever my computer starts it says press a key to start from USB and i do but then it boots windows, is there any was to clear my hdd and restart or comething? Please Help!!