computer won't post, 1 long beep, 2 short beeps.

[Tetras]

Any recommendations for a PSU?

For a 6600 XT?

The latter PSUs are for if you want to upgrade it later (550 is fine for your card) and the ATX 3.0 one is for running an nvidia GPU like 4070 Ti.

My basket at OcUK:

• 1 x Super Flower Leadex III ARGB 550W 80 PLUS Gold Modular Power Supply - Black (SKU: CA-063-SF) = £71.99
• 1 x Phanteks AMP 550W 80 Plus Gold Modular Power Supply (SKU: CA-09P-PT) = £79.99
• 1 x Seasonic Focus GX-650 650W 80+ Gold Modular Power Supply (SKU: CA-06V-SS) = £94.99
• 1 x Super Flower Leadex III 750W 80 PLUS Gold Modular Power Supply - Black (SKU: CA-061-SF) = £99.95
• 1 x be quiet! Pure Power 12 M 750W ATX 3.0 80 Plus Gold Power Supply (SKU: CA-14S-BQ) = £118.99

Total: £473.90 (includes delivery: £7.99)​

The Phanteks AMP is very similar to the Seasonic (it is built by Seasonic).

 

[doggystyle]

Thanks everyone after a long battle I'm pleased to announce the PC is working again. It was in fact a faulty PSU.
Due to financial and some time restraints I bought a cheap PSU from amazon, although I'm likely going to return it for a better one.

Thanks again.