BSODs/Crashes can be caused by Software or by hardware problems. If you have hardware problems (a bad motherboard, bad CPU, a bad hard drive, faulty RAM) then an install will likely fail too; your computer would need repaired/parts replaced.
But if the problem is software (OS is damaged or compromised in some way) then a fresh install should still work because none of the faulty software is used. Your DVDRom must be set up first on the boot order so that your hard drive is not read for start-up instructions. Instead your computer uses the basic instructions stored on the W7 DVD and should boot up to the W7 installation menu without problem. At that point you should select the command prompt and completely format the hard drive (everything will be gone, all your programs, all your settings, all your data, everything). Then you perform the install and a fresh OS is put on your computer hard drive. At that point you start over, you setup your ID, you install all the programs you use or run in the background (like a good anti-virus program), and then you scan for viruses any data you had backed up and you copy that back to your hard drive.