A little help with DVD+R Playback problem?

I have downloaded ISO's of Windows Vista and Windows 7 from the internet for repairing purposes these last few days. I burnt them onto blank DVD+R discs using the Windows 7 Windows Disc Image Burner and a Nero 12 trial. For some reason, after burning the discs, when I insert them into my disc tray, none of the discs are read; but when I play the discs on another computer, they all work perfectly. When I had Nero, I burnt a couple of discs, and they worked; could it be the Windows Disc Image Burner's fault? Can anyone tell me why all of this is happening? My disc tray is not faulty, I have tested other media, and it is read perfectly. I have also tried booting the discs with the BIOS set to Optical Media as the first resource or first media to load, with no avail. Also, the discs are new and in mint condition, with no scratches or anything of the sort. Thanks in advance!