How do I fix a xbox 360 slim with the red dot of death

cody kiesanowski what your Xbox has is a variant of the dreaded RROD. There are a few things you can try and do. Open it up and clean it out. There could be dust/debris that could cause this. Aldo, check the optical drive. Apparently, it can cause the RDOD. Of course, you could also try a reflow which might bring it back for a month or two but ultimately it will still fail. The failure of this is caused by the processor and /or this:

A dead or disconnected HDD

Cold-Joint between the CPU/RSX

A dead power supply

Overheating

Corrupted NAND Flash

You most likely have issues with your GPU processor. It is a flip chip design, and the issue could be the solder bumps between the IC and the substrate. A reflow might fix it for a while but even reflows are very limited. RROD are caused by the design of the processor, not necessarily by bad or cracked solder joints. The only repair that would fix it permanently is a new BGA. Try Reflowing Xbox 360 Motherboard - iFixit Repair Guide] and you may have to change the approach a bit by adjusting the heat. It is a hit and miss situation and most first-time failure with this is caused by not applying to much heat, whereas to much will totally remove the IC's. Anyhow, the biggest reason for failure to reflow is not enough consistent heat. There is a fine line between reflowing and absolutely melting the solder, so one needs to be aggressive without going overboard. If nothing else, get a couple of temperature probes and see what heat you generate. Replace the thermal paste but remember that thermal paste alone will not prevent a RROD. Apply it according to their specs and it should not give you any issues.

Here is a very "quick and dirty" explanation of what causes most of the RROD. It is not always a failure of the solder balls which connect the Flip Chip BGA package to the motherboard. It does happen and you can see why on here More commonly however is that the failure is due to the chip design itself.

As you can see the "bumps' are what actually connects the die to the substrate to make the chip complete. If these bumps fail the die does no longer make contact with the substrate and thus no contact with the circuit board. The chip has failed.

Here you can see the space where the bump has failed and no longer makes contact. We are talking microns of space here. So, a bit of pressure on the top of the die potentially close the gap. Same with a reflow, it may allow some of material from the bump to reshape and starting to make contact again. The heating of cooling of the chip during use is what will eventually cause it to fail again.