If you don't have this password, then you should have the seed that was generated when you first created the wallet, depending on the length of the seed you may be able to import this into Electrum.
Currently electrum supports a 12 word seed, if yours is longer or shorter than this you may have to look into alternatives.
I was using differend software wallets at the time when Electrum didn't even existed and I don't remember them giving you a seed when creating a new wallet (think of MultiBit Classic for example) so either old software wallets didn't give users the opportunity to generate private keys from a multi-word seed or I totally missed this option (which is possible since I was really unexperienced at that time). In the first case however, OP won't be able to recover the wallet because he has no seed to use.
Hope you're well - Essentially I have an old netbook with (I think) the ORIGINAL bitcoin client installed, not even Bitcoin-QT. The HDD is intact and I'm currently backing it up. I tried to take the wallet.dat file from that HDD and import it into electrum but after research it looks like this isn't the way to recover it.
May I ask the best way to recover it? My current plan is to clone the drive then try to run the drive in a laptop that works.
Kind regards
Before you do anything else, you should make a copy of your wallet first.
Is the console available in your bitcoin client? If so, you can try:
1. Click 'help' -> 'debug window' -> 'console' tab
2. If you wallet is encrypted, unlock it by typing walletpassphrase "your wallet password" 600
3. Type 'dumpwallet privatekeys.txt ' without the single-quotes.
Wallet keys will then be dumped to privatekeys.txt in readable format.
Create a new wallet in Electrum, and use sweep function to sweep the private keys.
If that doesn't work, download newest Bitcoin Core from https://github.com/bitcoin/bitcoin/releases
Run Bitcoin core once, then stop and close it.
Replace the wallet.dat in C:\Users\YourUserName\Appdata\Roaming\BitCoin\ with your wallet.dat
Run Bitcoin Core with -upgradewallet as argument.
As this gentleman pointed out, your best option would be to recover the private keys of your wallet in a readable format and then sweep them into an updated version of your favourite software wallet. Electrum can do it for you as long as you can supply the private keys of your old wallet. Those keys (if not encripted) give total control over your money so absolutely don't use any online tool or things alike to extract them! Only do that on your computer, possibly using the same wallet (and same wallet version) you were using when you created it.