Unfortunately your information is not very clear, so you need to help by answering some questions. Even more answers may be needed from you after this...
techhahn wrote:I was trying to install MAC distro on my pc
Just out of interest, is this a Linux distro? I'm not familiar with that name...
techhahn wrote:by mistake i formated 995kb partition.
What was in this partition originally - was this your Windows 7 "drive C" or something else? Please explain.
You don't really mean "995kb" - that must be a mistake. Do you mean 995GB?
I expect that this was a "quick format", but filesystem metadata has been lost (overwritten)

techhahn wrote:Now im unable to boot my pre installed windows 7
Based on this comment, I
expect that you've formatted your original bootable Win7 partition - I also expect that it's 995GB in size.

There are techniques to
try to recover any files (e.g. your photos/data) from that partition, but that will not make your Windows partition bootable as normal again.
techhahn wrote:im also unable to reinstall windows again.
Why not?
If you have no backup

then you may need to either buy recovery DVDs from your machine vendor, or buy a new retail copy of Win 7.
Those are my comments - I'm not a Windows expert, so other board members might have different suggestions...