No, according to Apple support document ht204592 "Use your iMac as a display with Target Display Mode".
The iMac (27-inch, Late 2009) and iMac (27-inch, Mid 2010) allowed either a Thunderbolt or DisplayPort connection. You would need a HDMI 1.4 to DisplayPort adapter for that.
The later iMacs (Mid 2011-Mid 2014) only allowed a Thunderbolt connection. If the iMac behaved as a standard Thunderbolt display, then there are adapters that could make it work (HDMI 1.4 to DisplayPort, Thunderbolt 3 add-in card and PCIe slot to power it, and an Apple Thunderbolt 3 to Thunderbolt 2 adapter).
But I don't think the iMac behaves as a standard Thunderbolt display because I can't find any reports of successful attempts to connect a Thunderbolt iMac in Target Display Mode to a PC running Windows.
If the iMac does not behave as a standard Thunderbolt display, then it means the macOS must be sending video in a non-standard format over the Thunderbolt cable (not as a DisplayPort stream inside a Thunderbolt stream). Windows won't have the software to do that unless Apple writes a Windows driver to do it but that won't help you because you don't have a Thunderbolt port.