Before you do anything else, please read my two posts here:
post31992.html#p31992
post62813.html#p62813
You will likely just need to import your wallet.dat file into a full client (and it is highly unlikely that it will be password protected as Bitcoin Core did not have that feature for another few years at that time) - but the two most important things to take from my posts are:
1.
Don't share your wallet.dat file with anyone; if you do, you are giving up the private keys which control your bitcoins and the person you share your wallet.dat file with will literally own your bitcoins. In the unlikely event that it is password protected and you think you can remember most of the password there is a
reuptable service which may be able to assist you but you use it at your own risk.
2. Make a copy (or copies) of the wallet.dat file before you do
anything with it. Don't back it up into the cloud, but do back it up onto a couple of USB sticks. This way if you mess something up or delete it, etc., you can just copy and paste it back from your USB stick to work on again.
Once you have managed to restore your wallet send the bitcoins to another wallet to ensure that if anybody else does get their hands on the wallet.dat file it will be useless and empty. I would highly recommend a hardware wallet for that amount of bitcoins but these are on backorder almost everywhere.
In the meantime you might consider using the
Bitcoin.com wallet to store your bitcoins - if you have a computer and a mobile device you can install our wallet on both of them to set up a '2 of 3' wallet, which basically means you will need access to both devices if you wish to spend your bitcoins. It's technically not as secure as a hardware wallet, but it's a hell of a lot more secure than storing your bitcoins solely on a single computer or device that might be susceptible to malware, etc.