I have recently been attacked badly by a virus. Unfortunately I did not had an AntiVirus at that moment(I understand that it was a very practice by me.) Now after reinstalling Windows I have tried to install Avast but whenever I install Avast It shows up a blue screen prompting the error message of memory dump and restarts. I have tried to install it in Safe Mode too but the problem remains the same. I would be very thankful if someone could give me a good idea how to deal with such a condition. Thanks.
Your best bet would be to take the drive out of the machine, put it into an external caddy then use a second machine to create a backup of your data before reformatting the drive.
Actually you don't need a second machine. Buy a new drive for your machine. Swap the out the old drive and install Windows on the new one. Put the old drive in a caddy and use that as an external hard drive/backup drive for your data.
It won't reinfect your new drive as it's not a boot drive. You can also delete the remains of the Windows folder and Program Files folder just to be sure.
Avast is almost helpless when you have already got serious virus.
Leading anti-virus vendors have special solutions in live-cd or simple .exe format to cure system without anti-virus software installation.
For example, Kaspersky Rescue Disc
or CureIT from Dr.Web - no installation needed, just one file.