user117030: back in 2012 I've acquired a small amount of bitcoins, which as far as I remember I saved in a wallet on instantwallet. I wasn't following what was happening with the bitcoin until I listened lately about its value. I also found out that instawallet does not exist anymore since it was hacked in 2014.
Apart from a URL on instawallet, I have a Bitcoin address and some kind of a private key. Could somenone please tell me for sure if there is any chance to recover my bitcoins or should I just forget it?

user13866: Recovery using a private key
If your private key looks like a proper Bitcoin private key, you can recover control over your money.
A private key is just a large number. There are several different ways of representing that number.




Representation
Example




Hexadecimal
E9873D79C6D87DC0FB6A5778633389F4453213303DA61F20BD67FC233AA33262


Base58 WIF
5Kb8kLf9zgWQnogidDA76MzPL6TsZZY36hWXMssSzNydYXYB9KF


Mini private key
SzavMBLoXU6kDrqtUVmffv




(Don't use these values they are just examples)
Note the specific lengths and the specific mixtures of characters. I think WIF normally starts with a "5". Your private key needs to match these characteristics.
Wallet Import Format (WIF) is probably the most useful.
You should be able to choose a wallet and "import" or "sweep" your private key.  Sweeping is considered safer because it works better with normal backups and recovery-phrases of the new wallet.

Instawallet
If you used Instawallet, it seems unlikely that you have a true private key.
See https://en.bitcoin.it/wiki/Instawallet

Instawallet's service learned that its security was compromised and on April 3rd, 2013 closed the service. Those with funds in their Instawallet can file a claim form to get their funds.

This sort of issue is why custodial wallets are inadvisable for long term storage.

117030: <p>back in 2012 I've acquired a small amount of bitcoins, which as far as I remember I saved in a wallet on instantwallet. I wasn't following what was happening with the bitcoin until I listened lately about its value. I also found out that instawallet does not exist anymore since it was hacked in 2014.</p>
<p>Apart from a URL on instawallet, I have a Bitcoin address and some kind of a private key. Could somenone please tell me for sure if there is any chance to recover my bitcoins or should I just forget it?</p>
 13866: <h2>Recovery using a private key</h2>
<p>If your private key looks like a proper Bitcoin <a href="https://en.bitcoin.it/wiki/Private_key" rel="nofollow noreferrer">private key</a>, you can recover control over your money.</p>
<p>A private key is just a large number. There are several different ways of representing that number.</p>
<div class="s-table-container">
<table class="s-table">
<thead>
<tr>
<th>Representation</th>
<th>Example</th>
</tr>
</thead>
<tbody>
<tr>
<td>Hexadecimal</td>
<td>E9873D79C6D87DC0FB6A5778633389F4453213303DA61F20BD67FC233AA33262</td>
</tr>
<tr>
<td>Base58 WIF</td>
<td>5Kb8kLf9zgWQnogidDA76MzPL6TsZZY36hWXMssSzNydYXYB9KF</td>
</tr>
<tr>
<td>Mini private key</td>
<td>SzavMBLoXU6kDrqtUVmffv</td>
</tr>
</tbody>
</table>
</div>
<p><sup>(Don't use these values they are just examples)</sup></p>
<p>Note the specific lengths and the specific mixtures of characters. I think WIF normally starts with a &quot;5&quot;. Your private key needs to match these characteristics.</p>
<p><a href="https://en.bitcoin.it/wiki/Wallet_import_format" rel="nofollow noreferrer">Wallet Import Format (WIF)</a> is probably the most useful.</p>
<p>You should be able to <a href="https://bitcoin.org/en/choose-your-wallet" rel="nofollow noreferrer">choose a wallet</a> and &quot;import&quot; or &quot;sweep&quot; your private key.  Sweeping is considered safer because it works better with normal backups and recovery-phrases of the new wallet.</p>
<hr />
<h2>Instawallet</h2>
<p>If you used Instawallet, it seems unlikely that you have a true private key.</p>
<p>See <a href="https://en.bitcoin.it/wiki/Instawallet" rel="nofollow noreferrer">https://en.bitcoin.it/wiki/Instawallet</a></p>
<blockquote>
<p>Instawallet's service learned that its security was compromised and on April 3rd, 2013 closed the service. Those with funds in their Instawallet can file a claim form to get their funds.</p>
</blockquote>
<p>This sort of issue is why <a href="https://bitcoin.stackexchange.com/q/81240/13866">custodial wallets</a> are inadvisable for long term storage.</p>
