My data for the last 2 years has disappeared. I have not upgraded or changed the survey in anyway. How can I retrieve this data?

can you please provide us more info ?
which version of limesurvey are you using ? what kind of server ? What do you mean by "disappeared" ?

The version is 1.92+
What I mean when I say disappeared is: All the responses that were present for the survey for the last 2 years were available until last month. Now, only 7 responses from this month are present in the database.
It is on Linux server

someone probably deactivated the survey and then activated it again. see:
www.limesurvey.org/manual/Closing_a_surv...survey_-_what_now.3F

Yes, that has been done several times earlier also. Is there anyway of retreiving the data??

It is still in the database (the true database server, like MYSQL, or postgresql.. ).
It's a table like :
lime_old_survey_{id of your survey}_{ date }

How can I retrieve these responses back to my survey?

see :
www.limesurvey.org/manual/Closing_a_surv...survey_-_what_now.3F

but it could remove your last answers. If you can't do it by yourself, consider buying the services of a limesurvey partner:
www.limesurvey.com/

Did you read the link that Louis was posting thoroughly?

www.limesurvey.org/manual/Closing_a_surv...survey_-_what_now.3F

Help! I accidentally deactivated my survey - what now?

If you closed your survey accidentally it is important that you don't change anything in the survey.
Then, and only then the following steps will work.
Activate your survey again
Go to the "Browse responses for this survey" menu.
Click at the "Import answers from a deactivated survey table" button.
Choose your source table.
Click at the "Import responses" button.

However, as your version of Limesurvey is ancient I can't tell if this feature already existed in "1.92"