The little I know about bootloaders is restricted to grub. I haven't read
enough about how the wubi installation boots or the windows bootloader to
help you there. It will cost you more in time and pain to try and trouble
shoot the bootloader than to do a fresh install, but don't be afraid to try
it if it's something you're interested in learning about. You just have to
be willing to put hours into it and you have to be prepared to make mistakes
that are non correctable. In other words, make a complete backup of your
entire system and data that you know you can restore from in case you make a
catastrophic mistake.

But first a few questions:

You said the system boots into windows? That would mean the bootloader is
working, so it's just that the option to boot into ubuntu is gone?

Do you have /home on a partition of the physical disk or a virtual disk
file?

By "regular installation" do you mean repartition the physical disk and set
up to dual boot?

How much free space do you have on your hard disk?

Are you comfortable on the command line?

Please try to be as specific as possible.