Windows 7 Installation – help needed!

Good day everyone!
I only have basic knowledge about computers and stuff, so please help me out with the technicalities of installing my new OS. Before I obtained Windows 7 in 64-bit, my machine was working on a 32-bit version of it. I have 16 GB of RAM, but I often use only about half of it more or less around 8 GB. Now that I have Windows 7 in 64-bit, I've experienced a problem in its installation.
It seems to be asking me for some driver and gives the message that nothing is found. I have also installed Ubuntu in it, and I'm not sure if this is the cause of the problem.
I have previously installed Windows 7 64-bit in my computer, but due to a virus problem, I've uninstalled it and reinstalled the 32-bit instead. Now, even though there doesn't seem to be a virus or something, it cannot locate the driver.
Please help my solve this problem.
Any ideas or suggestions will be greatly appreciated.
Please let me know of what you think.
Thanks!
